Sedna's minions have to be inherently weaker than other generals considering her regen and minion boosting auras. The survivability of Sedna's minion is really high.

And her other skills are so good it makes you wonder what to do.

However, in my experience, a minion build with Sedna works wonder if you don't have an AoE teammates to take on the opponent team general because otherwise you'll get swarmed by the ennemy and lose every fight easily.

Exemple : trying to fight minion Oak with Heal and Pounce is asking to die in a painful way as Sedna.

They are probably better then Shamblers and arent terrible - but the fact is that all of her other moves are 10x better then Yeti summoning. Heal, Punce, Healing wind + silence and maginifence silence and + hp/movement. All better then Yeti's easily.

Full minion spec Sedna can be quite effective at killing any demigod. Especially if you can jump them with a teleport while they are trying to capture one of your flags. The only real counters for this is Parasitic Egg, TB's and Erebus' aoe stuns.

Then I must be playing against a lot of weaker players because only a handful of players give me trouble. You being one of the few. I only consider myself an above average player and expect that once more good players show up it will be harder to get kills. On the otherhand, I expect that in those situation they will either leave me alone and go after my team mates or try to gang up on me.

In my opinion, most Sedna players think Yetis suck because their dependance on Heal + Pounce prevent them from fully realizing the power of a full Minion Spec.

If your not playing 1v1 it really matter what your teamates are taking. The only problem with a Minon build is that if the opponent has any speed enchacements then he can just walk away from your minons at almost anytime. Sedna's problem is that she has no slows so people just tend to walk away when they get in trouble. 

If you've got a Regulus on your team who's taken Shrapnel Mines, Maim, Poison Daggers or Mark of the Betrayer or a Eberus with Bite and Charm, Torch Bearer playing Ice, generally any Oak player as they all take Penitence and Surge of Faith, or a Unclean Beast that that takes Posion claws and will save his Foul Grasp till the person is running way then you can kill demigod quite well. The key is teamworks and politely mentioning that you'll heal him, if he stop people from running away when their weak. The damage output of minion is incredible espically if you've bought the right gear and taken the right favor item. With Ring of Divine Might giving plus 10 damage to all your minion (Which end game is basically +100 damage over your 10 minions.) you can be come a incredible force and I've seen demigod die just trying to reach Sedna in the middle of her minion swarm. 

As always the key to victory is teamwork.