Defense is not useless. It cant fend off a large fleet, but fully developed it can holds its own against 90% of pirate attacks and be a real help to defendding fleet wehn larger forces attack. I usually build 4-6 hangers,1-2 repair bays and rest are turrets

I have played a few games now. I managed to hold my own until I got greedy and attempted to annex one planet too many. I thought I could rely on my defences but they really are useless without a fleet nearby.

Personally, I would rather have more effective defences that do more damage rather than simply “stall for time”. We don’t build defences for that reason alone in reality; they are also designed to HURT the enemy as well.

Hell, it’s like building a load of farms in Warcraft II to prevent the enemy from getting to your base too quickly. It has no place in space!

The only time Gauss is useful is if the enemy just stands there going "Duh".

I love watching single ships just fly right THROUGH all the turrets, only one or two actually FIRE on it (the rest just ignore it), and it doesnt' take more than 25% shield damage.

I play with locked teams now just for that reason

I think once you have a Peace Treaty, missions should be optional at the very least.

Until about 4 hours ago, I didn't agree with the OP, but now I have seen what he means. Defending is underpowered. Whats all the more embarassing, is that it took a easy AI to show me this...

Let me explain, I was playing Vasari, 4 players(3 of which are AI, 2 are Vasari, and the 3rd is whatever gets the Robotics cruiser). I was ranked number one for economy, Militarily I was number 3(although I was ranked number 1 in defenses), and number 2 for Empire. I was engaged in a 2-on-1 with the other 2 vasari's on my northern flank. I was holding, and in some cases making gains, and using my superior economy was able to maintain pirate attacks against both of them. My southern flank was absolutely silent. It was basically being held at a single planet, with a tac. score of 35, all of which was invested into turrets and hangar defences(If I recall correctly there were 15 turrets and 5 hangars), and it had it's own small defence fleet(made up of about 10 heavy frigates, 5 heavy cruisers, and 2 carrier cruisers), the next system down had dockyards so I could start pumping out reinforcements if I had too, and there was a "reserve" fleet nearby(about 2 jumps away), made up of 7 carrier-cruisers and 2 carrier capitals and about 5 anti-fighter frigates.

Well... the 4th faction attacked my planet. It warped in with no less than 5 of the carrier-capital ships, 2 of the heavy battleship type, who knows how many carrier-cruisers, and then a whole mess of frigates of every type. Now at this point I'm thinking "I can hold them," and then I saw them disgorge all the fighters and bombers they had. My own fighter and bomber wings dissappeared VERY quickly. As in so fast, that in less than 30 seconds they had small craft superiority, now normally this wouldn't be so bad, the turrets had a lot of overlapping fields of fire, so I was feeling good, except that the entire force sat outside of the turrets range, while the siege frigates flanked around them(I had the turrets arranged in a semi-circle so that they posed a threat to any force that came in through the 2 phase-lanes) and immediately went for my planet. The fighters and bombers ripped the turrets to pieces one at a time(it took no more than 3 minutes until the wall of turrets I once had was only one or two heavily damaged turrets off to the extreme flank), while my attempt to move my fleet to attack theirs failed utterly. Of course I ordered the aforementioned reserve fleet to move in(I didnt realize that 2 jumps would take so long) and the orbital shipyards on the next planet over quickly spun into life.

Now, keep in mind at this stage in the game both logistics and cap ship crews were nearly maxed out on my side, and most of that was being used to hold against 2 attacking Vasari players, so I didn't have much to spare. With the turrets neutralized, the main fleet moved in and began either assisting in the orbital bombardment of my planet, mopping up remaining ships, or destroying whatever was in orbit, before the reserve fleet could even arrive(it was in the next system over at this point), the bulk of the enemy fleet was already moving on to the second planet(I.E. the next line of defense, where they repeated this process in largely the same manner, although at a slightly slower rate as they HAD in fact taken casualties... not much mind you, but enough to slow them down by maybe a minute or two). I of course resigned, as I was quickly down 2 planets, and they were moving on to my 3rd and 4th unimpeded and were soon going to be in my home planets gravity well.

Some of you may accuse me of sucking, but considering that was my 8th or 9th game of sins since release, and the previous two games I had dominated the map rather well(including games v. normal and/or hard AI), I don't think thats the case(and what the hell kind of easy AI was that? That AI was definitely a lot smarter than the other easy AI's I have faced). Regardless, I realized somethhing:
1 - Turrets don't have enough range. When a massive warfleet can jump into a system, and move out of the field of fire of your turret and then just spam fighters at you without sustaining much casualties, you know something is wrong.
2 - Turrets don't do enough damage. I understand they are not meant for anti-fighter duties, but when the fleet warped in, they were in range of maybe 5 of my turrets, and my immediate reaction was to order all that were in range(and more via click-drag) to open up on the first cap ship I saw. It sustained a fair amount of damage(about 1/3 of its total health) but it was very soon out of range. I wouldn't have minded too much if I had destroyed it, or at least got it down into the red).
3 - Using fighters to fight fighters and bombers doesn't work. Hanger defenses cost too many logistics points for what they do. I had 6 fighter wings and 4 bomber wings. The bombers were gone first as they attempted to go up against the fleet, while the 6 fighter wings faired a bit better against their fighters, did some damage I'm sure, but then dissapeared as I was easily outnumbered by at least 4 or 5 to 1 (fighters).
4 - Planets for whatever reason don't have any on-surface defenses. Now this one doesn't make sense to me, you would think there would be some sort of defense shield around the planet, and maybe some anti-orbital lasers... nope, none whatsoever. First space-based sci-fi story that I've heard of where this isn't the case.
5 - There isn't an anti-fighter/bomber turret that you can anchor in orbit around your planets.
And I probably realized a few other things, regardless, here is my solution to the problem:

1. Turrets - Increase cost by 1 logistic point, double range, triple damage.
2. Anti-Air Turrets - One logistic point, current defense turrets range, decent amount of damage.
3. Increase number of flights or squads or whatever you want to call them that the Hangar defenses generate(I'd say allow them 3, but 4 might make more sense).
4. Allow the construction of anti-orbital defense lasers and planetary shields under the planetary improvements thing. It doesn't need to be awesome, but it should be good enough to make bombardments take longer/be a lot harder.
5. Allow us to "mine" phase lanes, but only those that have your influence lines running across them. Make it so that they do a fair amount of damage to non-friendlies moving through the phase lanes(and they change allegiance if the enemies influence lines overtakes your own), and perhaps add in a new type of counter-mine ship which you can send in advance of your fleet to disarm them(this would take some time naturally), to help slow things down and give you a chance to react.
6. Scalable Fleet Supply - I don't know exactly how this would ideally work, it could go by number of opponents or number of planets or some odd combination of the two, but it should be put in to the game somehow. Ideally, it would scale to the largest allied enemy force(unless you are the largest allied enemy force, then you use your and your teammates combined fleet supply as a benchmark). I.E. if you're playing a 4 player game, and you've taken the lead and are fighting the other 3 back, and they all decide to ally to push you back, you would be facing a force that could be 3 times larger than your own. If you haven't managed to make a big enough dent into them yet, this means they have 3 relatively stable economies with production rates about 3 times your own with a fleet cap about 3 times your own. Basically an impossible to win against situation because A-Your economy is outclassed, B-Your rate of production is outclassed, and C-You're dragged down by their weight of numbers. There is no way to fairly alleviate A and B, but C can be fixed relatively easily.
7. Defense fleets - see above poster...

Just my ideas anyway. I'm still pissed that something like that could happen.

That *wasn't* their main fleet though, they jumped a second fleet in right after they had cleared out most of my stuff and started to move on to the next system. The second fleet didn't have quite as many carriers/cap ships, but it was larger from what I could see.

Also, I wasn't expecting 1 planet to hold, I was expecting one planet to thin them down, and the next planet to hold in the event of a main fleet attack, hence the reason why the second planet in line was heavily defended as well. And I didn't have that many planets(IIRC I had 8 planets), losing two planets(one of which was an ice world - the only ice world I had), and then watching them phase into 2 out of the 3 lava world's I had, pretty much meant that I was screwed.

The point of defenses in any RTS is to slow down your opponent long enough for you to come back. The same is true in Supcom(which btw, since you brought up I will make the point that even the Tech 1 defenses have enough range to cover a considerably large sized chunk of the map.). Obviously they aren't very good at doing this job if it only took about 7 or 8 minutes to clear out a single system and move on to the next(and it only took them maybe 3 minutes to take out the planet itself...), especially if it takes almost half that time for a fleet to cross a single gravity well and initiate a phase jump. In this case, I was Vasari, so I probably should have had phase stabilizers or whatever so I could make a large scale jump across the galaxy, but what about the other 2 factions? If they had suffered the same attack and were in the same situation I was in, they would have been just as screwed as I was, and would have been more screwed then I would have been if I had the phase stabilizer.