Hypothetical question: In real world racing, would it be anywhere near reasonable to build and maintain a race car powered by a tiny engine with massive turbo if bigger engines were allowed in the first place? (XRR engine vs. FZR engine)
I dunno about today, but I'm fairly sure there was an era when formula one engines could be either 3 litres or 1.5 litres with a turbo, and plenty of teams went with the crazy turbos instead of the 3 litres.
Imho they should have exactly the same tire size and engine size. The different sizes in tires are very hard to balance, as one could think of. Having a 2 litre turbo engine against 3.6 litre NA with 500hp is just not realistic as these cars aren't exactly high-tech anyway.
A twin turbo might make it more interesting but the power isn't the main problem in this class. It's the tire/fuel consumption which are totally different in every model.