For a character with a Strength dependent class, a Strength cap is a Strength penalty because it directly limits the things at which they are supposed to excel.
I wasn't aware that the barbarian class, the paladin class, and any fighter using a non-finesse melee weapon were considered niche builds.
So, the issues are that they disincentivise player choice and they promote stereotypes so we see more of the same kinds of characters again and again. Sounds like a bad idea to include it in the base game to me.
There is when "because realism" is only being applied to act as a limit to one sex, to stereotype and pigeon-hole one sex. If realism is that important, give proper "reality-reflecting" penalties to male PCs as well.
None of the classes you cite require strength 20 to work. Most male versions will not have 20 so the niche builds is that upper strength. We have a group of 14th level characters and none of the warrior classes have 20 strength. Tell a lie, there is a Female thri kreen.
No class requires a 20 in any stat to "work."
Or an 18, really.
Or, for that matter, a 16.
Might as well cap all stats at 14 then.
Maybe a 10 or 12, just to be safe.
Your hyperbole is not logical.
My warlock/rogue has 15 dex and 14 cha and works just fine. Doesn't mean I begrudge others having higher stats. They just aren't necessary and you can spend your points elsewhere. She has 17 int.
Hyperbole is typically intended for humor more than logic.
Not everyone uses points.
Also, just because no class needs a 20 in any given stat, that doesn't mean that characters of one sex should be prohibited from having a 20 in a specific stat while members of the other sex have no limits applied to them at all. Imposing limits on one sex because "realism," while ignoring the effects of realism on the other sex is by its very nature biased and inequitable.
BTW - promoting maxing strength could do more to promote Fighter monoculture that forcing people to look at other more varied options. In my experience, my players don't want to repeat themselves.
I fail to see what this has to do with the idea of only allowing males being able to reach max Str.
Forcing women to be weaker than men doesn't change that, it just means if you want a max strength character, you won't choose to make the character female.
In my experience "forcing people to look at other more varied options" rarely works out well. This is a hobby, people play it for entertainment. Forcing people to do things they don't actually want to do just means they'll find someone else to play with. Or stop playing altogether because it's no longer enjoyable.
In my experience it works out just fine and I've played with a lot of people. I can recall whining to my brother about having more racially varied groups in 1983. I don't recall any problems since reaching adulthood. Tell a lie, one player showed up with a half celestial whose stats were mostly 20+ in 3e and the DM asked him to try again but he did and it was fine. He still plays with us today.
So, if I understand Celebrim's stance on this: Because real women are physically weaker than real men, and physical strength should never, ever be used as a measure of a woman's worth (because that's sexist), wanting a fantasy woman in a fantasy game to be as strong as a fantasy man is also sexist?
Because you are devaluing real women by having fantasy women who can compete with fantasy men on equal terms in areas that rely on physical strength in your fantasy game?

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.