Erm Wight and Mage of the top of my head.
45 to 80 hp iirc.
This hp bloat and weak saves especially wisdom and intelligence is why we use spells like hold person a lot. Command or tashas etc if not.
And Fireball kinda sucks.
Gladiators always been tuned high in terms of damage. Use wisdom saves or better yet intelligence saves they get wrecked.
5E is default easy mode so they cranked up danage to compensate. 5.5 bloated the HP on a lot of monsters.
One thing that might doom it. Once the suger rush wears off the amount of piwercreep makes DMs job harder.
If people don't want to run it you're in trouble. Players I suspect like the power creep.
5E appeal originally was comparatively simple.
No one knows. I'm not expecting 5.5 to do as well because it's a revision.
Generally revisions are better than the original but they don't sell as well (1E vs 2E. 3.0 vs 3.5).