I think monsters are undertuned in 5E. By quite a lot. Max PC hit points would only make the problems of the edition worse.
IMHO It is the PC's that are
overtuned.
Re:
Monsters and PCs, if anything need LESS HPs, not more.
Agree. It's not so much about the length of the combat. But the consequences for the PC's getting hit.
Ok, so the big bad was dusted in under 6 rounds... At any point during those 6 rounds were any of the PC's in danger of being killed?
Is taking a single hit from an alleged "Mythic" monster even a concern for any of them? If not, then how is that monster "mythic"?
I think HP in general is an overused defensive factor for both PCs and NPCs. It leads to number bloat which is just going to slow the game down. Bigger HP pools leads to seeking more damage which will eventually lead to the need to inflate them again.
I'd much rather have more active mitigation, recovery, and avoidance features than just treadmills of bigger values.
In other RPGs that don't have exponential HP increases; HP = meat points, and they typically have some other 'meta' currency to mitigate the occasional bad roll or lucky hit: "hero points". WFRP fate points, CoC luck points etc..
D&D traditionally does not have a 'hero point' meta currency, because for D&D the HP increases per level (HP Bloat) fill in for that. Which of course has always muddled the waters of: 'what do HP represent"...
HP Bloat is D&D's 'Hero Point' meta mechanic. Hit Points in D&D are 'meat points' and 'hero points' all rolled into one.
Pre 3e D&D had limits on that though as PCs stopped gaining hit dice around level 10 or so... Not so much in the post 3e game. Now PCs gain hit points every level.
This of course leads to scaling issues with the math in every subsequent edition of the game. Which is why they all have issues the higher in level the game progresses. Stuff like CR, and the right amount of HP for x at high levels are off because it is just too much too playtest and calculate ahead of time given all the variables introduced into the system via spells and class abilities.
The easiest solution to the scaling issue is to side step it.
IMHO people were on to something with the E6 mod for 3.x edition D&D.
One can do similar for 5e, Like this guys "5e Heroic" version:
Why mod D&D 5e, isn't is perfect already? A lot of people get frustrated with high level D&D and tend to avoid it altogether. Typically there's 3 reasons for this: 1. Combat is too s
purplelizardman.com
Of course there is a strong segment of D&D fans that find such restrictions after a given level abhorrent.
So in that case, Just pile on the HP...