I don't really follow that flow of logic. I've never seen a feat that said, either explicitly or implicitly "and by the way this is now the only way to accomplish this". I'm not even sure I'd buy that argument about a 4e feat, to say nothing of 5e. Even if I did, what you're claiming is implicit is only so if you look at these feats from outdated action resolution frameworks. 5e works differently from that.
I'm just relaying what I've seen. If I have a shallow 20 ft wide river that has water tumbling over rocks and is therefore difficult terrain, I may not think of the option as a DM that the character could dextrously jump from rock to rock. But now? If we use this feat I guarantee someone will raise a fuss if someone tries to cross without the acrobat feat.
Maybe I just need better players. Unfortunately I kind of like them. Heck, I liked one of them so much I married her.
This is the heart of 5e. DM empowerment. Rulings over rules. If you feel you have a responsibility as a DM to maintain verisimilitude and internal consistency in your world, you are empowered to do so, to the explicit extent that you can declare that a PC's proposed action has no chance of success. This is made as clear to the players as it is to the DM. Presumably your players also care about verisimilitude and internal consistency; if not they might not be at the right table.
Ultimately I don't disagree with you ... but (you knew there was a but, right?) I think these feats are different. They've kept stealth and hiding vague for just this purpose. So the DM can make rulings on how they envision stealth working in their game. They can make it nearly impossible to hide in combat, or they can be extremely lenient. I try to strike a happy balance.
But the new "stealthy" feat breaks that rule. It specifically states conditions (if you have cover and move less than 10 feet) that you can remain hidden. According to the wording of the feat, you can walk right in front of the demon with truesight and not be noticed.
Can I override that as a DM? Of course. I could also say that I just decided that your greatsword only does 1d6 damage because I think 2d6 is too much. Either case I would consider a house rule (overriding the rule), not a ruling.
Now this I can absolutely respect. I'd been giving this some thought and I think one of the biggest problems is the use of conditions. Because conditions are such a hard-coded and clearly-defined part of the game system, I don't think they should interact in the more nebulous world of ability checks. Certainly not to the extent that these feats suggest. I'd like the
option to decide if your action, your target and the context of the scene in question warrant a specific condition like
charmed or
frightened. There are obvious situations where they don't seem to be warranted; I'd like the riders to be a bit more nebulous and "DM determines results of the ability check"-esque. I don't blame them doing so; it's an easy resolution and I still don't really see how either effect would be game-breaking in any game run by a DM with half a pulse. It's just that I don't think conditions and ability checks mesh well together. So yeah, I've come around to the idea that the conditions ought to be removed from Diplomat and Menacing.
They're still not anywhere near as terrible as Performer though
See? We do agree on some things.
I dunno. I think Frightened is more powerful in combat. A fighter with a decent charisma could frighten several opponents and keep them locked down and ineffective (or force them to run away) for the entire fight while the rest of the party pelts them with ranged. I know people (particularly in AL) that would look at this as being an optimal build, and if you didn't use it as written would be upset.
How do I know this? Because it happened on a regular basis in LFR. Chuck would say something like "I intimidate Gorax the Dragon. [insert some ridiculously high intimidate check]. He is frightened and can't approach and can no longer come into melee range of the party, etc". I got away with overruling it because I ran the game day, but
technically his intimidation should have worked. His one skill check should have made a tough fight a cake walk. If I had allowed it, every fight with only one or two opponents would have ended the same way. Menacing adds that power to 5E.
If the many of the tricks and stunts one could accomplish with skill use were laid out for players and GMs alike, and the skill feats only served to enhance these options instead of providing brand new capabilities, then their codification wouldn't get in the way of improvisation.
I agree. I wouldn't mind some additional advice on how to handle skills, I think it would be helpful. Maybe walk through a scenario showing off each of the different skills. I could even see having examples for two DMs with different styles of game. Describe how two different DMs could rule differently and why.
If you haven't listened to Jeremy Crawford's podcast on stealth, I'd recommend it. He explains why they left stealth open, and that at one point they did have very detailed rules on how to handle everything and decided not to use those.