Alternative take, 5E lorewise is more streamlined and useful than the metaplot bloat of 2E. What counts as a "Golden Age" in lore quality is entirely subjective, unlike sales or player activity.
I think that's kind of a half-truth. Subjectivity definitely applies more to lore than sales or player activity, but it's obviously not correct to say it's "entirely subjective". It's also not correct to suggest people playing 5E prefer 5E lore to the lore of previous editions - in many cases, in fact, 5E's lore is simply a recapitulation of earlier editions (as one might expect) and people are often using previous-edition lore or their own settings or the like.
5E's lore has a few issues which are worth discussing.
1) The
amount of lore in 5E books has been steadily declining, particularly recently. This obviously has nothing to do with "streamlining", because we're not seeing elegantly streamlined, well-summarized lore. The writing is no better than previous editions, no more streamlined, no better summarized. There's just less of it.
2) 5E's non-MtG-derived lore has, I would suggest, more often been self-contradictory than previous editions.
3) There's the issue of the value of MtG settings. Most of them have lore fundamentally incompatible with D&D, which has to be worked and hammered into shape to try and achieve some level of compatibility. The success with which this has been achieved is debatable, but certainly a huge amount of 5E's "lore/setting" output, particularly by page/word count, has been dedicated to recapitulating Magic: The Gathering lore, rather than adding new D&D-specific lore, or recapitulating/updating D&D lore.
4) In part due to the objectively decreasing page-counts and word-counts dedicated to lore/settings (whilst the page-counts for monsters and adventures increase), even within supposed setting-books, a lot of 5E lore is simply very shallow/cursory.
5) There's also been an issue where lore-writing has been
fundamentally ill-conceived, in part due to 5E starting out as an "Apology Edition" designed to regain grogs, before realizing maybe that wasn't such a great idea and having to engage in a fair amount of retcon within the edition. I don't think any edition has actually had to do that before.
6) Compared to all previous editions, 5E has been severely lacking in terms of "original" lore. Virtually all of 5E's lore has either been from Magic: The Gathering (which again, is not highly compatible with D&D, lore-wise), or from earlier editions. 1E and 2E added a ton to D&D lore/settings, for better or worse, because they originated tons of settings and lore. 3E at least added Eberron and a bunch of races and their associated lore. 4E completely redid a lot of D&D's fundamental lore (and featured classes which were more lore-heavy than 5E's ones, I'd suggest), and many of those changes found their way into 5E. This obviously may change. We've been told 5E is going to have 1-2 original settings in the next 1-2 years. But we've also been told that it simply might not, and we've been given the impression that WotC has cancelled at least one, possible multiple original 5E settings.
None of this is a disaster.
But the OP is flatly right, objectively. 5E is a "Silver Age" rather than a "Golden Age" in terms of lore. I came in ready to disagree with the OP, note, but unfortunately they are simply correct. Attempts to say "Oh it's all subjective!!!" fail because well, it isn't all subjective. There are some facts involved, and even where subjectivity is involved, subjectivity doesn't negate or invalidate criticism. It's not a magic shield you can hide behind. Especially not if you don't actually provide an alternative to the criticism. Merely saying "subjectivity" is in fact a non-argument. It's the prelude to an argument. If you don't actually provide said argument, though, you're just raising your hands for the orchestra to play, then running out of the building trailing music sheets!
5E or 5.5E/6E could easily redeem itself here. Turn around the increasing tendency for setting books to not actually have much setting in them (which is reaching a shocking new low with Spelljammer only managing 64 pages of lore/setting & rules combined), and add a couple of actually-novel and cool (even if niche) 5E settings, and we could easily say 5E was the best edition lore-wise since 2E.
Will that happen though? It already looks like they're gearing up to gut Planescape, based on the most recent UA, and to go for the unintended (if we believe Monte) disaster that was his post-Faction War-take on Sigil. That's not a good sign.