Honestly, I could probably use the SCAG, but only when divorced from the rest of Realms canon.
You mean like the bit in the back, where it specifically instructs you how to use the crunch for a variety of different worlds? The SCAG furnished me with several different Solamnic Knight options for Dragonlance.
I do get where you are coming from an the SCAG, specifically, is a better example of that argument than Volo's. I've only ever been in Realms as a player where I've DM'd a lot of different established and homebrew settings and could find LOADS in Volo's to use in my stuff. Even my not-used-since-3rd-ed caveman setting.
I know that some of your argument about this is about it being the FR as standard setting and marketed as such but the DMG makes it pretty clear that you can make your own world off the bat and gives you load off stuff for doing that. I mean all of the lore specific stuff sometimes jars with me too (I hate the new Barghest/Gnolls lore, for example. In my most played homebrew world, Barghest already have a very specific role and Gnolls aren't mindless killers but a clever race who fill a 'Bounty Hunter' niche.) but as it's fluff it tends to be the easiest thing to ditch. If you literally bought Volo's for the crunch and never read the fluff, you could still be reasonably happy with it as a purchase.
I realised that the reason I'm even pushing this is because I feel like by taking this stand, you've denied yourself a great product over a line drawn in the sand between granular levels of universes of fiction and that kind of makes me sad. But as long as you're enjoy the game you have from the three core books (I make an assumption there) then that's all good,it's the way the game was originally intended to be played. Maybe you're right, really D&D would have been better served if we'd never had Official Campaign Settings at all. But that bird flew a long time ago. Given that polls seem to indicate that a large majority of people homebrew, maybe it's a non-issue.
Side question: When 3rd ed came out, was anyone bothered the assumed setting was Greyhawk? I'm just curious but it never occurred to me before.