1 of each capital ship capping at level 15 might be a nice Scenario / Victory Condition, since there'd be a lot of focus on capital ship placement. I'm not sure level 15 is all that necessary though since most caps after level 6 are pretty resilient.

It seems like doing that would make them like titans. It also feels like you are comparing a single capital ship to a titan and a starbase. Those two were made  powerful to counter / repel capitalship spam. The real strength in capitalships is using their abilities to bolster your fleets strength / survivability and weaken the enemies.

What could work is balancing titans like how they are in EVE, anything below capital class ... would have modifiers against titans ("inaccuracy" because of the amount of guns if you like) to nerf their effectiveness against smaller targets and make them dedicated Cap/Titan/Starbase/Structure killers

personally i like how titans are forceing greater use of capitols, i never liked how much of an after thought they felt compared to massed frigets and crusers. i hardly ever built more than one cap ship factory before, or bothered to build more than a token force of cap ships, now i always build a cap factory closer to my front icase i lose a cap ship. i would be sad if, as you suggest, frigets were set up as pure Cap/Titon/Starbase/Structure killers.  where is the interest in that blanket stratagy, where frigets and crusers counter everything an caps/titons are just for people with an ego.  it makes more sence to me that titians counter massed frigets and can destroy starbases, leveled cap ships increase fleet surviveability and can hold the line against titans, frigets en mass take advantage of cap ship buffs, supply the dps/utility to a fleet and therefore counter cap ships (not becuase of inherent counter mechanics) but becuase of pure numbers.  frigets should be the lowest on the rung.  the fact is that a highly leveled cap ship is powerful, useful and, now with titans, nessisary. titans mean that there will be more use of cap ship raiding early game in an attempt to gain xp/ slow titan rush.  if any change needs to happen in the way of cap ships. their supply limit should droped to a more reasonable level OR the cost of cap ship cre should be droped considerably (to fully upgrade the cap ship supply is much more expensive then it is to resurch and build a titan) and some underused caps should gain ether fleet buff abilities or titan counters.  some currrent cap ship spells also don't work on titans which is disapointing.  i don't belive ion bolt works on a titan for instance.