TBH Summoning is extremely powerful simply because it does not require main stat to function well, you can build a tanky buffer with tons of CON and 10 summoning and it will still be able to do quite a bit more damage than that setup could ever do otherwise and will be unkillable. Heck you will get rallying cry and dominate too as well, not too shabby.

Incarnate is pretty powerful, it's not a player character powerful, but it's a lot of damage for something like 4-5AP you spend in the beginning of the fight and it's unkillable too, pretty much.

IMO summoning is exactly where it should be, maybe it's even a bit too powerful simply because of that no-main stat binding caveat.

2 summons? That would be outright broken, unless Incarnate is severely nerfed, but that would be uncool imo, I like one uber summon.