They can perfectly play with summons (fist, wasps).

Yes, and you can also throw magic arrows. But no, the fist is immediately ruled out; it's a parody. The wasp swarm sometimes works due to the initiative reduction, but it's a very situational combo. So, light magic + summons for Haven is not a good idea...

Exactly this kind of division is made in the Wargame Edition mod.

WGE is a global mod. You can change schools there, which also changes creatures and, in the future, hero skills. And then everything is tested for balance. But simply changing things is a completely different question.