Don't know so much about the balance in older editions but the absolute numbers are pretty much irrelevant, as long as the relative numbers are somewhere comparable. Does not matter if the boss has 10hp and I do 1 dmg per round or he has 1000hp and I do 100dmg per round.

Anyway: I agree that Larian should put more trust into the CR balance, that is already there and just builds appropriate encounters with them.