CR 20 melee bruisers are few and far between for a reason (and many of them are immune to fear).
Like a Balor. Oh wait, he's
only level 19. My bad.
But I'm not saying don't set up the encounter! I'm just saying if you don't want unexpected outcomes, then don't allow for unexpected outcomes.
If you don't want the heroes to be able to face down the foe, then don't let them face down the foe. You're the DM. It's OK.
I try to avoid cheating. I'm just trying to also avoid "I win" buttons for the PCs.
I can always just ban these feats from my home game or modify them so they don't stack with expertise or other bonuses (like Observant). But that won't work when I'm running a game at a store for the public campaign.
These feats give PCs at a relatively low level the possibility of powers and capabilities that epic level monsters don't have. That seems broken. I'm OK with a level 20 PC being really good at what they do, but these feats give PCs magical abilities that aren't magic, have no limits on the number of times they can be used
So for example, a mid level party can now intimidate a Balor round after round and kill it with ranged attacks while never being threatened.
It was these kind of abilities that killed much of the fun of 4E for me, except they're worse. At least in 4E the abilities were frequently limited to encounter or daily.