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.
They do indeed matter, because in all RPGs (at least all i ever played and its a lot), output and input do not scale in the same speed. Does not matter weather its DnD, Pathfinder, Skyrim or anything. The higher the performance gets, the shorter and deadlier the fights are. Thats because of stacking synergies. Everyone remembers Level 1-2 fights in TTRPGs that took like 15 rounds and were pretty close. As the PCs are getting stronger, the fights will shorten significantly, since the PCs can more effectivly focus and CC enemies down.
Due to the highly increased performance of both PC and NPC in BG3, the low level fights are already affected by this effect. Fast, short and deadly for either side.
Most people will have beaten EA without any major problems, so i do not think the game is too hard. But it is less exiting in terms of combat. For the most part, after the seeing how the first round of combat goes, you generally already know that you have won or lost, since you either managed to achieve your win condition or you didnt and be doomed.
