Well literally anything is better than what you proposed, because what you proposed is so flawed from the start. You're suggesting that we take some of the most powerful things that already exist and combine them into one ability (and, as noted by someone else, render one of those effects irrelevant).
I admit the only reason we have this problem is because Cait Sith stole what would otherwise be Phoenix's signature ability. If you want to take that and make it better or different in some way, it needs to be in a way that's balanced. I could see Arising someone without weakness and giving them some powerful buffs at the same time. But not the entire party whilst also nuking the enemy. That's just too much stuff packed into one ability. As noted. If it was just one person and particularly strong? I could see that, as it would have different use cases from Cait Sith's ability.
The framerate issues in this game don't really have much to do with how big or how many polys a model has (in any normal case, it's the latter- scaling something doesnt really affect performance much). I would much rather have a regular summon than an astral flow one I will hardly ever see.See: phoenix is a huge model so I don't want it to be out for like logistical/lag/framerate reasons. I like the Odin/Alex type of smn, but it should be closer to Siren in execution/reality.
I do respect and share the desire to make pacts with the remaining avatars, but going nuts with crazy powerful ability ideas is not really the way to go. I doubt SE would solicit ideas from us on something like this, but if they did, I'd rather we put our best foot forward when it comes to ideas of how these summons would work.