3. "10/min duration buffs" - same as above. Why would suddenly all NPCs will have this specialized buff? After all it works only 1,5-2 hours at this level and let's say when "its buff time" they have more important buffs to drink/cast.
I don't agree with this counter-argument.
You are talking about a 12th-level superhero in an urban setting where everybody gossips about everything. Surely this guy is famous by now, right? Surely some (probably ALL) of the enemies he's facing have heard of him, and probably many of them know he's coming; I hope your CR 12-ish enemies are not just sitting around on their piles of loot waiting to be slaughtered - they must know there are dangerous superheroes and they must be preparing to face them, right?
I think that justifies having many of these humanoid foes preparing specifically to face a famous superhero who is well-known for his sundering prowess.
And you're also well-justified in having many of these villains be smart enough to set up alarms (even silent alarms) - using even better high-level solutions too - to alert themselves that superheroes are coming, in time to cast buffs that last hours in preparation for an impending, life-and-death battle for survival against terrifying odds.