Is D&D generic like GURPS? No.
Is it more generic than Earthdawn? By a pretty large margin, IMO.
Earthdawn works for Earthdawn. Which is fine, because that's what it is designed to do. You could probably hack it to do other things, but it would probably entail significant work and you'd likely lose many of the things that make Earthdawn good in the process.
D&D supports a variety of settings. Can it support anything out of the box? No. However, it does support a range of fantasy significantly broader than what Earthdawn is meant to do.
I'd say you're overestimating the margin between ED and D&D mechanically.
The real difference is simply that the writing for ED takes time and effort to embed the classes into the world or Barsaive. D&D could absolutely have done the same. It doesn't, but instead it makes a huge number of incredibly specific assumptions about the world, which I've discussed, which generate a hyper-specific implied world (though the exact nature of said implied world varies from edition to edition - 3.XE being the broadest and closest to "generic fantasy", I think, esp. if official-optional rules are in play).
ED didn't get popular enough, but I daresay if it had, we might well have seen it support other settings. I disagree with your claim it supports a narrow range of fantasy, at least if we're talking mechanics. That is an impossible claim to accept when Vancian casting exists, when HP exist (and there's no mechanics to get around them - you just knocked out about 90% of literary fantasy settings right there - I notice Worlds Without Number DOES have a way around HP - execution attacks - which are different to and more appropriate to most fantasy than CdGs), and so on.
I can't say ED supports a wider range of fantasy mechanically, but I can say it is at least as broad.
One strength of “Tightly thematic” is that the DM can more tightly tie in classes and races into the setting. Part of what makes this easier is the possibility of simply excluding certain races and classes.
“Kitchen Sink” gives players more freedom to realize their characters. This isn’t always about “having a super unique character”. Sometimes, a player is in the mood to play something different, or wants to try a different mechanic.
This is extremely poorly argued and deeply unconvincing, I'd suggest. It uses the counter-factual we've already dismissed, too, of "all artificers belong to an order of mage hunters". That's utterly ludicrous nonsense when we look at many actual pen and paper RPGs that actually embed the classes into the game. Earthdawn embeds the classes into the world - does it require classes to be members of a specific order? Nope (well not in the corebook IIRC, expansions might). So we can instantly dismiss your theoretical artificer mage hunter example with the non-theoretical and factual existence of Earthdawn. Sure, you
can do the contrary - Rifts does a fair bit, for example - Rifts has some classes which are tightly specific, some which are more generic, and so on, though all are tied to the world more than 5E classes - but you're not required to, nor is it fully typical, and if you're not required to, the argument is null and void.
There's also no contradiction between Kitchen Sink and tied to the world. I mean we just mentioned Rifts... Rifts ties every class to the world (some harder than others, but all have ties, none are mere "power frameworks"). Rifts is more Kitchen Sink than literally any other game in existence. There is no D&D setting remotely approaching Rifts in terms of Kitchen Sink-itude (not even Planescape).
So the only way that tying characters to the world can be an issue in the way you describe is if the player
does actually want a "special snowflake" character - i.e. a Drizzt-clone in Dark Sun or the like, and they're not willing to take half-measures (i.e. he HAS to be a Drow and HAS to a Ranger and so on). I admit such players exist, but I've only found them above about age 16 when they were people coming in directly from "pure" roleplaying (aka "OC roleplaying") and has specific OCs they wanted to play - and even most of them are flexible.
Even then it's only an issue if the setting isn't broad enough - you could be a Drizzt-clone in Rifts.