Not a strawman. You literally seem to want every class to have some feature or other special rule they can use for their benefit in basically any situation. In any situation everyone will have a fancy bespoke tool to use. That is wanting them to be 'good at everything'.
Nope. Not what I said, not even a vaguely charitable reading thereof. Having something meaningful to contribute to combat does not mean "literally all combats, you WILL be a star." Having something meaningful to contribute to socialization does not mean a "special rule" for literally all possible social contexts and it is ridiculous to assert that that is what is being said.
Combat, exploration, and socialization are not "everything," and "having something meaningful to contribute" is not the same as being "good" at it. The fact that you, again, have enforced a false dichotomy of "literally incapable beyond absolute rock bottom baseline" and
superlative skill is an error. There are many,
many more possibilities on a spectrum between the two.
Also, why would we even have skills and ability scores if they're never good enough to be used for anything?
Because having at least one meaningful contribution is in no way a guarantee that it works in absolutely all possible conditions and states of affairs? Huh, imagine that, it is almost like I'm
not calling for absolute universal perfection, but rather clear and at least somewhat defined areas of
competence. Which is a far less dramatic request than "good at everything" and far harder to knock down...almost as though my position were being characterized in a extremist and illogical manner so it could be dismissed without actually engaging with it....
As I've already pointed out, yes it is: when put in terms of the power level of the party as a whole, boosting the bottom tiers also boosts the overall average power level of the party. That's power creep, even if not every character gets to share in it.
Then power creep cannot possibly be a universal evil. If you intend to define the phrase this way, you're going to have to accept that some of the time, power creep is a straight-up good thing. Because, for example, 5e is an increase in Fighter and Monk power relative to 3e. By definition, if you think 5e does better at full-caster vs non-caster balance, you are in favor of at least some amount of power creep. Importantly, this means calling it "power creep" is no longer a slam-dunk "that's as many as four tens" argument; you will have to explain why THIS power creep is bad while 5e's other, baseline forms of power creep were not.
If your party is in a city where magic and-or its use is banned then your Wizard becomes an ordinary person (or an outlaw, your choice

). If your party is engaged in a mass melee then your Rogue becomes little better than an ordinary person. If you're trying to sneak somewhere then your tank Warrior-types become ordinary people.
As others noted upthread, casters being denied in this way gets players bloody rioting. Do it to a Fighter and that's par for the course. You present as symmetrical a situation that is fundamentally not and the fact that you refuse to see the asymmetry is part of the problem.
That said? Your example of sneaking is exactly on point. Yes, that is the kind of thing where a Fighter (that has not chosen to invest any resources into it) SHOULD find herself with few options, and possibly nothing more than the baseline. Because "exploration" means a lot of things, and stealth is only one small but often salient component thereof. The un-stealthy plate-wearing Fighter may be forced to doff her armor, putting her in greater danger in order to lay low. Or she may try to leverage her eagle eyes to be overwatch for her more stealth inclined teammates, at the cost of being unable to directly assist should an area of her greater expertise (like combat and surviving within it) suddenly become relevant. Or she may need to rely on her teammates, like the covert-ops Warlord who can guide her through some basic exercises he knows to get ready for something like this, or the Wizard casting a muffle spell on her to ameliorate her weak ability to conceal herself (but in so doing, committing some or all of their concentration to it, making further choices tougher). Conversely, these choices may be useful in that the Fighter's mighty thews and indefatigable back may be incredibly useful for getting past blocked paths (DW's Bend Bars, Lift Gates), an example of a well-defined contributiom to exploration (and sometimes yes, even specifically stealth challenges) that IS NOT omnicompetence in all possible exploration challenges.
Noe of this means those characters can't contribute anything. They're just mechanically limited for a while.
Not all contributions have to be backed by game mechanics in order to be relevant.
I tire of Fighters and Rogues etc. being separate but equal. It has a long, long track record of being continuously unsatisfactory for the non-casters and always taken over the variable strident objections of casters. You know, the ones who actually have to give up some amount of power to those denied it. Funny how that happens.
D&D characters are to me just ordinary people in the setting who have some cool abilities tacked on; and at times when those cool abilities aren't useful they are - and can always act as - the same ordinary people they always were.
Unless, of course, they're Wizards, Druids, Clerics, or Bards. Then they're
magical superbeings adventuring alongside horse jockeys.
And you're always, ALWAYS better off making sure Angel Summoner is well rested and ready for action. People rarely, if ever, say, "man, I know our Wizard and Cleric are totally out of spells and can't do anything but cantrips, but thankfully we brought a
Fighter so we can keep going even without that!" That's another facet of the asymmetry.
My namesake character is a 10th-level Fighter who can bring some hard-core badass to any party he joins, but when fighting isn't appropriate I still find ways for him to contribute just by speaking or acting as himself the person rather than himself the Fighter.
Cool.
Question: Assume your character was, instead, a badass Paladin. Same (or as close as possible) personal story arc. (Perhaps a devotee of a more athletic, Strength-based dudebro deity like Kord.) What would change about your statement above? Does being a Paladin somehow impede or restrict your ability to "find ways for him to contribute just by speaking or acting as himself the person rather than himself the [Paladin]"?
Because unless you are asserting that being a Paladin (or hell, even a friggin'
Barbarian, with the right subclass anyway, looking at you Totem Warrior) actually PREVENTS you from "finding ways...to contribute just by speaking and acting as...[oneself] the person," you would seem to be admitting that you are relying on stuff literally anyone (as a player) could do with literally any character, making the choice to be Fighter superfluous.
It ain't rocket science, and it doesn't need game-mechanical support.
The sustained dissatisfaction from a significant chunk of the audience seems to belie this assertion. Because isn't it curious how it's always the ones upset about the gap being told to suck it up, and always the ones totally cool with the current state of affairs that get to decide who gets what?
I should also point out that sometimes the best contribution a character can make to an in-game scene or situation is to Do Nothing and Stay Quiet. I hit this the other night: our party are engaged in some intricate spying and info-gathering in an off-world city. My PC has been invisible the entire time and nobody outside the party knows she's even there, allowing her to better act as a spy and scout; so when we got into a bunch of negotiations last session my entire contribution was to sit quietly unseen in a corner the whole time with my (un-needed, as it turned out) lie-detection device on high alert.
And yet you were contributing, because you had been given DM favoritism via a magic item that (surprise, surprise) replicates a low-level but useful spell. Had your little lie detector gone off, would you still have Done Nothing And Stayed Quiet? I am more than a little skeptical about that.