Or you know, give them (perhaps conditional or limited) ability to deal more HP damage! I really don't get this desire to invent mechanics for things that already have mechanics.
Because that’s not any different than what they already do. It’s not really more exciting. Or not meaningfully so.
But spells that are about dealing damage still do it via hit points.
Not all spells that remove an enemy from play are about hit point reduction. This is one of the complaints about the fighter/wizard divide… so many more avenues are open to the wizard.