when considering 20th level, I honestly don't think you can overdo it, because there are so many factors you won't have in your whiteroom analytics. Does 323 hp seems like a lot for the fighter? On paper it might, but then you factor in:
1) How often will the fighter have an energy resistance against an attack from numerous areas.
2) how many attacks will be flat out stopped by party shenanigans? (rerolls, blocking attacks with things like walls of force, just being flat out immune to an attack through a wish, preventing the monster from getting close enough to even attack, etc)
20th level parties have so many freakin tricks at their disposal, that even without a lot of optimization I would expect them to take on way stronger threats than their on paper stats would often indicate, so no I would not tone down the numbers. 323 hp isn't the fighter having 323, its trying to model the innumerable ways the fighter will be able to tank things that you don't have written on the paper.
1) How often will the fighter have an energy resistance against an attack from numerous areas.
2) how many attacks will be flat out stopped by party shenanigans? (rerolls, blocking attacks with things like walls of force, just being flat out immune to an attack through a wish, preventing the monster from getting close enough to even attack, etc)
20th level parties have so many freakin tricks at their disposal, that even without a lot of optimization I would expect them to take on way stronger threats than their on paper stats would often indicate, so no I would not tone down the numbers. 323 hp isn't the fighter having 323, its trying to model the innumerable ways the fighter will be able to tank things that you don't have written on the paper.