Adding extra hp isn't necessarily a bad thing
It really is, in the overwhelming majority of cases.
For example if you usually blow up every enemy before they even get a chance to do anything
If that happens, chances are you have a lot of rescaling to do across the board, on several aspects of the game.
Well, the point I'm making is that it isn't a bad thing in some cases. If you're going to argue that the number of cases are small, that's fine, I mean we're arguing on the finer points there.
I'll give you a solid example, in Kingmaker at the end of the Varnhold Vanishing questline you fight a caster boss who has paper HP. I think every time I have ever fought this guy I have destroyed him in one round. Maybe he gets one spell off.
Just by giving this guy a ton more HP, you'd actually have to engage with his mechanics, i.e. the spells he might fire off. That would make for a much more interesting encounter.
Another example would be Mephisto in Wrath, by the time I faced this guy I was level 19 or 20 I think and again he didn't last more than one round once I got my MC into melee range.
It's just sad when you have an enemy that is capable of interesting gameplay but because he's made of paper he just gets blown up in 1-2 rounds and doesn't get to do anything.
The number of times I see Raphael get one-rounded in BG3 by a range of builds, some highly optimised, some not that optimised, it's just really boring.
Of course there are other ways to solve these issues, for example in BG2 a lot of bosses are given contingency spells to enable them to get their defenses up quickly at the start of the fight, and this makes things much more challenging without having to simply inflate HP. But apparently RPG developers are hard to teach these lessons to