Couldn't a lot of the flexibility problems for summoner be alleviated by allowing trance to stack up to 2 charges (and reducing its cooldown to 30s)? Tri-disaster could similarly carry 2 charges (with trances restoring one charge), but I'm not sure what a good cooldown would be. Of course, you'd still have to cycle through Bahamut to gain access to Phoenix. I think this would be a good compromise between people who like the current system and people who want to see the flexibility of aetherflow return.

I agree that summoner AoE being complex is enjoyable, but I don't like its current incarnation. If outburst was an instant spell and did not rely on ruination, I think summoner's AoE would be much more fun, still be pretty interactive, and wouldn't interfere with switching back to single target as much.