Removing things completely is almost never the solution. As someone who enjoys playing scoundrels /rogues in RPGs, I see literally no reason to remove them, you'd only be fucking over non-mages.
I think that handing out grenades that simply emulate mage spells is a poor way to balance this.
I would definitely prefer that non-mages should have the skill trees to be interesting without these kinds of add-ons.
As for grenades, they can stay, but they should have a unique role. It should be different from any other item or ability.
