I would say that they do not believe the Balor can be intimidated by mere mortals. Especially mortals that he has absolutely no reason to fear.
Now ... add in some creative use of illusion, some RP, maybe a thaumaturgy spell along with some deception checks? Maybe they can convince the Balor that Darth Bader (or whoever is in charge of the place) is pissed at his subordinate that is daring to his lord why he's personally escorting prisoners. It's called having a fun creative solution to the problem.
So even if the Bard tries anyways, with just his words and actions alone with no magical effects, no matter what he said or what he rolled, he would fail?
That isn't quite what you are saying, but it is pretty close. Intimidation only works if the situation seems reasonable and they've set up an elaborate ruse, like lying to him... which is deception.
In fact, passing yourself off as something else is the sole domain of deception so that wouldn't be an intimidation check at all. I agree with wanting players to try more, but "I'm scary cause I'm your boss" or "I'm scary because I'm a Divine Being" is vastly different than "I'M SCARY" which is the point of Intimidation.
King of the barbarians? Pah. Human champion of the Lord of Darkness? My bitch. Lord Palpatine? His heart is palpitating.
No one should be that intimidating.
But the King of Barbarians is that scary, isn't he? He can walk into a room and silence it with his pure imposing presence.
Is it just his rep? I doubt it, that kind of character is scary even if you have no idea who he is. So, there's got to be something going on with his stats right? Because you don't cheat so if he's scary he had to get that high intimidatin score somehow.
I'm poking at this because I completely agree with the conclusion that I want those beings to be scary as all get out, and my players shouldn't just be able to walk up and intimidate them. So, once something gets to be of a certain status or power, I tend to just stop letting non-magical fear work, if the situation doesn't fit. But, I do it by giving them a minor immunity to fear, a character trait almost. And you declared that cheating, but your alternative solutions seem to just be cutting intimidation out of the game unless the players are stronger than the individual they are intimidating. Which I feel goes too far the other way.
Which is all well and good. However the feat clearly says the character makes an intimidation check opposed by an insight. If the character wins, the target is frightened. You're ignoring the text of the feat.
That's fine. In fact, I agree. That's my whole point.
Since I've been grabbing your stuff, wanted to throw this on here.
This, for me, isn't to prove your wrong about the feats. Personally, I think Intimidating one thing instead of attacking is relatively weak, though it being limitless is a problem.
For me, a lot of these discussions are kind of missing the elephant in the room of "The players can already do this". If the Frighten condition isn't imposed by Intimidation, what do you do? If the bard has Expertise in Intimidation, rolls incredibly high, and gives a short, brutal message that chills you a little, but he's doing it to the Lich King of a Tyranical State, what do you do?
I want my villains to be fearless, people who are afraid in literature are generally the weak ones. But, I don't want to tell the player they failed, when mechanically and acting wise (if you enforce that which can be problematic when you have players who can barely string a sentence together when you put them on the spot) they should totally succeed and be a bad@#% themselves. He put fear into the Demon of Black Fire, that's what a roll of 35 should do, the impossible.
I see auto-giving the frightened condition as problematic, but even if they change that, it doesn't change expertise in Intimidation and what it might mean for a situation.
A couple (Diplomat, Menacing) seem broken. I see certain types of gamers stating that every high charisma character should take those feats and then proceed to stomp all over every AL encounter. Then complain because the mods aren't tough enough. So the writers ratchet up the difficulty where in order to survive, you have to optimize your character.
Charm isn't
that bad. Charm, per the rules, just gives them advantage on Charisma Checks and prevents the person from attacking them. Since it fails if they are in combat already and takes a minute to activate, it really just says "You spend a minute talking with someone and make a Persuasion check, if you succeed they won't attack you and you have advantage on all social checks with the target as long as they stay near you"
If that can possibly break an encounter, I'll say it was a poorly designed encounter, because this is not a compulsion. They like you, but they aren't going to put themselves in trouble for someone they just "like" without some fast talking and maybe some bribing.
With Perceptive, an 8th level human rogue or bard can have a passive perception of 30 and ignores light concealment.
Already essentially possible with per PHB. In fact, a level 8 Rogue or bard with Darkvision can have a passive perception of 26 (actually how did you get 30? Did you forget Expertise doesn't stack again?) and can see perfectly under all darkness conditions except magical darkness. Just need Skulker and Observant.
Again, not a lot of things being added that weren't already possible.
Though invisi-Rogue with Stealthy seems new, depending on the situation, the architecture, and how clever the player is. I could totally see someone with acrobatics just spidering across a high beamed ceiling in a dark hallway with deep shadows to get past that same 10 ft gap. So, it's only something that couldn't reasonably be done is highly specific circumstances. And despite that, movie and shows do show exactly that sort of thing occurring upon occasion, which is where I think it got drawn from