All your points are taken and respected. But this one...
First, you again frame it as though the person isn't going to have fun because they are not as good of a fighter as the other characters. You say: "I'm sure they will have a blast." Sarcasm aside, they might have more fun because their character - and here is the part that keeps getting missed - is good at something unexpected and good at fighting; not great at fighting and okay at a bunch of other things. See the scale there? Good and good vs great and okay.
I can hear the next phrase coming: But I can make great and good if I do this and combine it with that... And that is the other point getting missed - that player can and does because they are a min/maxer. If you feel obligated to build the great and good or great and okay instead of the good and good because your level of enjoyment in a role playing game will be lessened - then you are a min/maxer. (Or at least that is how the argument is being framed.)
It seems to be all or nothing with you, which confuses me greatly. Either I don't care about roleplaying because I am a min-maxer, or I don't care about my ASI's because I am playing a roleplaying game.
What you miss is the spectrum. I'm going to shift from fighter to barbarian, because Dex fighters are a thing and a lot of people might say they are better than Strength Fighters.
Let us say I want to play an Elf Barbarian. Why? Not because I want to min-max, but because I find the story potentials of an elven barbarian interesting. I can imagine some very interesting roles and thoughts from someone who has lived 200 years in the same forest, cut off from civilization.
However, that doesn't mean I want to be a bad Barbarian. In fact, being strong and dual-wielding troll-bone handaxes is part of my backstory, it sounds awesome. I can build some great stuff with this. Except, nothing in elf mechanically is what I want for a Barbarian. the lack of Strength and Con make me deal even less damage, miss more, have lower HP. Heck, if I was building this with the Standard array, I'd be looking at 15, 15, 14, 14, 10, 8 which isn't terrible, I mean, I can work with it. But my very first ASI at level 4 is going to be getting those to 16's, meaning I can't take feats which I love to take, because they are more interesting.
But, I could do a nearly identical concept with a Dwarf. Getting 17, 16, 12, 13, 10, 8. Same AC, better damage, better hp, better in every way as doing what a Barbarian does. So, now I am forced to answer a question. Do I care more about being an Elf, or more about being a Barbarian?
And I hate having to ask that question. I shouldn't have to ask it. But I know the system. I know how hard it is to keep playing with a 16 after 5th level. Every single time I've done it, I've been left longing to reach 8th level so I can get that flipping 18, so I can tilt into the more comfortable patch of bonuses. I'm literally expeirencing this right now with my rogue. I want to take feats, but I've got a 16 dex, and it is leading me to miss far more than I should, leading to me feeling worthless in combat. And I even could have gotten an 18 at 4th, but again, I love feats. I seriously do, they are far more interesting than these boring numbers, but every time I ignore those numbers, I spend the majority of combats twiddling my thumbs and missing.
So sure, call me a min-maxer, say I'm a roll-player who doesn't know what DnD is really about, but I'm sick and tired of making that decision. I'm sick and tired of thinking "wouldn't it be cool if- no, won't have the right stats" I want to role-play, and not have the game punish me for it. People are so worried about "humans with funny masks" that they are forgetting that DnD is Carnivale, and you should be changing masks with abandon.