Really? One summoned creature even when you have gone to the trouble of leveling up other skill lines? That's pretty bad. You can spam elemental totems, though. I think they should nerf elemental totems to 2 max per character and allow you to summon one creature per school of magic as you said. Problem is, at the moment you can rush summoning with Lone wolf (Summoning 10 on two characters at level 5?) and offset the lack of characters with multitudes of totems, plus give your characters tons of CON and WIT instead so they're also meat shields that run away to let their totems do the work.