Not that my opinion will weigh in a hell of a lot here, but, in my eyes the deformed seem alright as is. They have a decent amount of health but beefage doesn't hurt. They're good as tanks to take down tubes and sometimes vents.
As for dropping to just classics... I think that'd be just outrageous. It'll add no flavor. It's more fun having different types of zombies... a different strategy is required for each one..