I suppose this is why OSR is a thing. But I do think “everyone must have an equivalent combat value” is a pernicious failing in modern D&D that breeds many unfortunate outcomes.
Same could be said for the Thief's original design, re: breeding many unfortunate outcomes. The problem is that you don't see those outcomes as unfortunate, because they're subjectively so (in both cases), and you're in the extreme minority (to judge from sales of RPGs that at least TRY to balance this stuff against those that intentionally do not). I get that that may be annoying, but it doesn't make that any less subjective. Just sayin'...
I think a good case could have been made for a Thief-type class that was less-good in a straight fight, but better than Thieves actually were at stealthing and particularly killing from stealth. Backstab never, in edition, reliably did enough damage to take out guards and the like (who were as often 5HD+ as 1HD). Thieves were never good enough at stealth (again, in any edition, including 5E) that they made it reliably possible to sneak past guards in heavily guarded places, either. Certainly not at a level before the Wizard could solve the same situation with a few good spells (and often much lower risk to the party).
If instead of the Thief-as-total-wimp-who-isn't-even-that-skilled design of pre-4E, you'd had a design where Thieves were deadly commando types who also stole stuff whilst slitting throats (who are actually extremely common in pulp fantasy, note, all the way back), where they had some kind of insta-kill ability on unsuspecting targets (or at least silent-kill, even if it took a round or three of garroting or whatever), then I don't think the whole paradigm re: combat ability would have become an issue.
But the fact that they were both not actually good at their job AND frequently beaten at their own job by casters (and this was true in 1E/2E, it's not just a 3E thing) meant some kind of change was inevitable.
I did see a very good Thief in 2E once, but he was a case of massive magical item assistance. Without the items he'd have been by far the least capable (in any situation) member of the party.
I have to ask, too, were/are you a habitual Thief/Rogue player in pre-4E editions? Because my personal experience is that the people who liked Thief as it was in, say, 2E, didn't actually play single-class Thieves, or did once in a blue moon. Whereas I've personally seen people who played Thieves/Rogues since early 2E being incredibly excited and happy with the 4E redesign of Rogues to actually be combat effective (and they like the 5E design, though it's not quite as exciting for them), and I know from accounts here and on other boards, I'm not the only one who saw this with long-time Thief/Rogue players.