I'm surprised that it's the gladiator that stood out.. it's basically the same as the 5e14 gladiator- it saw almost no changes to 5e24.
The thug NPC statblock became pretty infamous at our tables. CR 1/2, 30hp, 2 attacks, pack tactics. But really, they have 5 hit dice. If we called them fighter-lite, they should be getting two attacks. Pack tactics, ha, well.. that's something else.
Same thing as above... gladiator has 15 hit dice! It's basically a level 15 fighter-lite, it SHOULD be getting 3 attacks!
Let's not forget 3e with its NPC classes, they were basically PC-lite: warriors had the same base attack bonus, but had d8 instead of d10 hit die, and no fun extras. I guess in short, they were operating by different rules already... PCs were "better" than the standard NPC.
I understand the weird "hey, why can they do that but I can't?" feeling players will get... but in the end, they are operating with different toolkits. Generally they're following the same core system rules, but the PC class are something special/different/atypical. I know it can creative a dissonance at times, but it may need to be explained to players that NPCs just have different tools than they do; it's the way the game is designed. A player only has to worry about controlling their one character- the GM has to handle every NPC. It helps that the NPCs are simplified, typically, to one or two-trick lite-versions.
Edit: a note on the HP disparity between PCs and NPCs... well yeah, hit dice, right? But if you don't mind widening the gap between PC and NPC even more (hey, the gladiator is already doing two dice of damage instead of one per swing) you CAN do as Mike Mearls (and many others) have suggested and lower HP while raising damage. ~35% lower HP, 35% higher damage. That'll put that gladiator at 73hp, much lower than 112! Of course he'll also be doing about 15 damage per hit instead of 11...