My though, as I was trying to get across in my Wall of Text post, was that's actually kinda a blind alley and why it's been so hard to make the fighter viable in D&D for so long. I point to the introduction of the Thief in Greyhawk as the genesis of the whole thing. The way I put it succinctly is that you could combine the Fighting Man & Thief, or, today, the Fighter & Rogue, into a single class - just give it all of eachother's non-redundant features (and, yes, Extra Attack & SA are obviously redundant DPR-generators) - and the result would be in no way overpowered or overshadowing, and it would better model characters from genre. But, it seems unthinkable to give up either class, and since both are so narrow in their abilities, they both remain non-to-barely viable choices, and road-blocks to creating anything better. Instead, things the 'fighter' should be doing get increasingly diced, broken out, and/or specialized in sub-class, feats, builds, PrCs, alternate classes, or whatever (even magic items have been used to inject perfectly reasonable martial abilities - like standing up quickly, any stunt man IRL can do it, but it took 'Acrobat Boots' in 4e, wtf?). Heck, as much as I like what 4e did with the Martial source, 'marital' itself, is unduly narrow. There's more to a hero in the fantasy genre than just fighting skill.
And, again, that's not the whole of it, there's other factors, other early decisions that have gotten propagated and calcified for decades into unshakeable dogma - often while, simultaneously, the underlying game-design reasons for them were undermined. For instance, in the early game, the Fighter & Cleric's ability to wear heavy armor was a huge deal, the AC gap between a guy in a robe or leather when everyone had random-rolled 3d6 DEX and the one in platemail & shield was huge. Ever since 3e, with high stats expected, DEX bonus to AC limited by heavy armor, and any class that didn't get such armor getting spells and features to give it competitive AC, heavy armor has been little more than cosmetic - sometimes even a distinct disadvantage.