Well, Grazzle is a pure spellcaster (that 1 weapon is mostly a support, so you can't expect him to be useful with weapons, just like most video game pure casters).
Well I play him as I see fit. I like the heals cause we needed them, but he can use some nasty spells but I also gave him 2 weapons. I charge in knowing I could use a spell and a weapon. Reading the rules I never found where it says you can only play one card that says for your combat check. In fact in the rules after you have chosen your skill aka strength for combat check using a weapon it says you can play one boon of each type. Well as I read that a spell is a boon and there is no verbiage that states in that paragraph that that boon cannot be played because it says combat. Again I like to look at these situation as if I was there. If I know magic and I know how to thrust a sword I will do both to dispatch my enemies it's not rocket science LOL.