Ideally, I want to see new versions of the Players Handbook for every new setting.
Eberron Players Handbook: Warforged race, Artificer class, the pertinent archetypes for core classes present, Psionics, diversity of religious traditions, reflavoring of spells for the unique Eberron cosmology, etcetera.
Dark Sun Players Handbook: Thri-Keen race, Elemental Cleric class, Psionics, Defiling Magic, harsh life, The Dragon, the unique cosmology of the Black and the Gray, reflavoring the spells, etcetera.
And so on.
Make these stand-alone all you need Players Handbooks, with a rewrite of the relevant core races (maybe with only one subrace given), and pertinent core classes (with pertinent archetypes), all the combat rules and so on, so there is no need to refer to the defacto Forgotten Realms Players Handbooks.
They've done exactly what you suggested. The PHB has the relevant core races - the ones
they say are the relevant ones based on the settings and feedback (and dragonborn, tieflings and such are optional and may not be in every setting).
And despite you continuing to say it, it doesn't make it true. The PHB, DMG, and MM are not defacto Forgotten Realms books. There are as many references to the other settings within them, and the references to the other settings combined outnumber the Forgotten Realms references. The very first example in the PHB is Ravenloft. Quotes from novels are mostly from the Realms, because they have the most novels and the most recognizable characters. But there are examples from the Dragonlance novels as well. Once you get into the classes, they talk about their place in each of the settings where appropriate.
Almost all of the setting material, Forgotten Realms or otherwise, is either quotes from novels, or examples. The only actual rule that is tied to the Forgotten Realms is the list of human races, which is still just an example ("In the Forgotten Realms, for example..."). Other than that, find me a rule in the book that is Forgotten Realms specific.
The APs are set in the Forgotten Realms (except, of course CoS), but the PHB, DMG, and MM are not. I agree that VGtM was a miss, both in the content (probably 50%+ I don't care for), and by releasing a MM that is really for all campaigns, but tying it to the Realms directly. I suspect you and I will have the same complaint about the XGtE - there's no need to release a book that is presumably for all settings (and/or includes material not appropriate for the Realms) in a book centered around a Realms character. Of course, if the history of the last two editions means anything, then they'll continue to dump everything into the Realms. But I really hope that's not the case and that they maintain separation for what makes Eberron, Dark Sun, and other settings (including the Forgotten Realms) unique.
In 4e they decided, for whatever reason, to homogenize everything. They wanted to design a niche for each race, each class, and do it in a "D&D" way instead of based off of material that influenced the game. So they decided to change the eladrin to something different, and replace most of the elves with eladrin, for example. And then infected every world (including the Realms) with this inane idea.
For 5e they figured out what D&D really had - the multiverse. Where different worlds with the same base rules are interconnected with the planes (and eventually Spelljammer again). And the multiverse, in D&D lore, is the home of the gods.
So you can
want to see a PHB for each setting, but you won't get one. You probably won't get a campaign setting book for each setting.
Like it or not, this
is D&D. This is the product that they decided best represented the history of D&D and the
whole of D&D players. Obviously, when you're playing to that large a group, you won't make everyone happy. In fact, I think it's fair to say that
nobody will be happy with 100% of what's published. But the goal is to try and make something that's at least 80% of what everyone wants.
From what I can tell (particularly based on our discussion in another thread), they've made you more than 80% happy. There were fewer than 100 sentences (not including the Appendix on the gods) that referenced polytheism, which was what you objected to, in the PHB. You're just choosing to focus on the less than 100 sentences instead of the book as a whole. Maybe you hate the cleric entirely. That's still probably less than 20% of the book.
So if you want to continue to complain about fewer than 100 sentences, that's fine, you're certainly entitled to do so. But don't expect it to change the designer's minds or approach. They've got a huge hit on their hands, and they're going to continue to build on the foundation they've laid.