Summon damage seemed decent to me towards the end game. It didn't that much when you initially got them. Boost helps them deal more damage, but I wish like Elskidor said that there was a short option for summon animations for IX and VIII (Can't remember if VII had overly long summon animations too). I'm less bothered by it in VIII because of the way boost works in that game.

In IX it would've been good if Boost just increased the summon power of the short animations and increased it even more when the full one comes up. Summons like Ark... Actually I might have to check on something. I think I remember that you could actually break the damage limit in this game, but only with Ark. I'll be back.