Let's apply this principle to PHB feats, shall we?
Athlete
* When you are prone, standing up uses only 5 feet of your movement.
* You can make a running long jump or a running high jump after moving only 5 feet on foot, rather than 10 feet.
These are both things the feat says the players can do, without condition. And yet... might the DM impose conditions, when they are appropriate? Is the DM being "adversarial" if they tell a PC with Athlete they can't stand up from prone after moving only 5 feet, because they happen to be 6' tall but the ceiling is only 4' off the floor? How about 3'? If a corridor is more than 5' long but only like, 1'6" wide, is the DM being adversarial to declare that the PC cannot run and therefore cannot activate that ability from Athlete?
Here's a better one:
Defensive Duelist
When you are wielding a finesse weapon with which you are proficient and another creature hits you with a melee attack, you can use your reaction to add your proficiency bonus to your AC for that attack, potentially causing the attack to miss you.
This seems fairly cut and dry, right? You get hit by a melee attack and still have the ability to use your reaction, you get to use this feat, right?
What about if your PC can't see the attack coming? An invisible attacker successfully sneaks up behind you and hits you with a melee attack? Is the DM being adverserial to say that the PC cannot use Defensive Duelist in this case? There's nothing in the rules saying you have to be able to see the attack coming. And yet, the implicit fiction of how the feat works is fairly clear. Does the PC get to use their reaction to react to and block an attack they couldn't possibly know was coming until it hit? Or does the feat confer Spidey Senses?
I could probably dig through some class features and point out times where the DM would be well within their rights to say "no, because..." (especially if they don't follow that up with "I said so" which such a ludicrous mis-characterization of our argument that it still kind of ticks me off), because the the game empowers the DM to make exactly those kinds of rulings all the time.
I don't care what kind of literal, rules-lawyer-y player you may or may not have; whether a home-game that's lasted years (if not decades) or a pickup game with strangers at a game store, D&D is a game that requires trust, and primarily trust that the DM will referee fairly and impartially in order to maintain an internal fictional consistency. Despite your best attempts at arguing at strawmen, we've shown pretty clearly that such rulings would easily be seen not only as fair and impartial but also perfectly logical by anyone with any sense in their head. Anyone who's going to waste the table's time and energy arguing with a DM because "technically the RAW says..." is not interested in playing a fair or impartial game (the very definition of a rules lawyer is someone who will twist the words as written to every possible advantage they can receive, frequently without care of game world logic) and does not belong at that table.*
*I'll own that I'm sure there are tables full of players who all play the game that way and find such rules lawyering to be quite fun; and more power to you. But if you are a DM and you're wringing your hands over a feat that threatens the verisimilitude you obviously care about because you feel you need to appease a rules lawyer player who will only allow the feat to be interpreted a specific way, the problem is with your player and out-sized influence you've allowed them to wield over the internal consistency of your world, not with the feat.
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As a final aside, I have to say that re-reading Skulker also made me LOL since it has the exact same kind of cognitive dissonance as Stealthy supposedly has (you could be hidden from a creature, pop-out while they're looking directly at you, miss with a ranged attack, and the creature doesn't even get a chance to see you).