The thing is, outside of message boards, I have never encountered a player that actually cares about these things relative to other PCs.
Wow, really?
I've been meeting them since I was like, 12, in 1990. Seriously.
But I suspect if you're honestly claiming "never", the issue is that you're framing it too narrowly. I've almost never seen a player say "Your character is overpowered and should be nerfed" (I say almost never, because I have seen it happen). But I often see players who are sad because their PCs suck compared to other people's PCs. Sometimes they express it clearly if it's discussed, sometimes they just assume that's "how it is".
Here's a good example for you:
For the last nearly-30 years I've played with some of the same people (30+ in some cases). One of them habitually played Thieves/Rogues for most of that. Whole of 2E, he never once complained outright about being crap compared to the other PCs (even though he clearly was). You could see he was a little sad about it sometimes, when like his awesome backstab did less damage than the Fighter did in two swings or whatever, but he never complained.
3E, he branched out a bit but mostly stuck to Rogues (indeed, every character he played was at least Rogue multi-class), and he did end up complaining a bit. Mostly because he just didn't feel as effective as he did in 2E (which is fair - the gap in effectiveness in 3.XE was a lot further), and actually felt like his PC was less skilled.
It wasn't until 4E, though, that he finally "tasted blood" - 4E Rogues were total badasses who were as good as other PCs, instead of frequently being objectively worse at stuff than other PCs (even their own stuff, sometimes). Suddenly, he learned how to optimize, and really enjoyed it. He totally loved 4E, had a great time, played the character he'd always wanted to play, and finally understood what he was missing.
In 5E, he started with a Rogue, but didn't enjoy it much, and has now tried a lot of classes (and is loving Warlock particularly). He's now clearly aware of the difference in effectiveness between characters, and tries to optimize his PCs much more now, because he can see that leads directly to them being more fun to play.
It's not like he's sitting around whinging about other people's PCs, but he is actively attempting to make PCs which are closer in balance, and is doing so because he knows it's enjoyable. You can see a similar pattern with a lot of the players. There's been a distinct drop in people willingly/intentionally playing "useless" characters, or even weak ones, as people understand what is going on more, and understand that being mechanically effective is, in most RPGs, more fun than not being that.
But in Shadowrun or Rifts the gap can be much wider and as GM you have to ensure that all characters are at least in the same ballpark or that the game regularily switches to allow different characters to shine.
Yeah it was Rifts that really made our group aware of it. Rifts itself highlighted them a bit, but always insisted PCs of different power levels could play together - and yes, they "could", but only in the sense that it was technically possible, rather than desirable or effective or reliably fun. The power disparities were bad in the corebook and just got completely insane by the time stuff like South America was out.
After that there's no way we could "not care" about PC balance at all. There are many games where it barely matters, or basically automatically exists, from CoC to most PtbA stuff, but in ones where it is an issue, it produces a more fun game for everyone if some attention is paid to it.
With 5E I intentionally only play support characters with my main group, because I don't want to be a spotlight-stealer, which might easily happen if I optimized a DPR or toughness and DPR-centric character (Warlock, Fighter). Especially as there's a lot of "shallow" optimization in that group (i.e. stuff that sounds good, but isn't that effective - still, you do see stuff like EB+AB, GWM and so on, they're not idiots).
What do you do if you feel your choices aren't as good or your character isn't as competent?
I haven't made an outright-bad character design choice or accidentally made an incompetent character since about 1993. If a PC performs suboptimally for me, it'll either be by design, which means I'm usually into it/enjoying it (for example, a number of SW D6 PCs of mine), or because I totally built the wrong character for the campaign (i.e. they're optimized/functional, but what they're good at is irrelevant - i.e. a Shadowrun Decker but the campaign features almost no Decking). Usually in the latter case it's fine because they're good at enough other stuff that it doesn't matter. But if they're entirely useless, I'd probably ask to re-roll/re-spec - one of my players often goes through 2-3 PCs in a campaign before he finds the one he really enjoys (which does seem to be connected to effectiveness).