Basically, they threw everything (Greyhawk, FR, etc) into one generic FR setting.
I would say this is the mistake. I'm okay with them deciding to have an implied setting, but they shouldn't have gone with an established one. Yeah, yeah. Nentir Vale.
What does "intentionally assuming" mean? Does it mean that even if other people suggest that it isn't really a Realms-only product you aren't going to believe them?
It means that I dislike the current strategy and use of the Realms strongly enough that I'm no longer willing to purchase product associated with the Realms. So, I'm not even interested in the content. It has Volo's name on the cover, so I'm very intentional in my assumption that it's explicitly for the Realms. If it was general purpose, it wouldn't be titled as though it were a Realms book.
5E is, mechanically, the best edition of D&D, to date. The team did an amazing job on the rules and I very much appreciate the effort and the fact that I have everything I need to play, pretty much forever. I think they're doing a very poor job of managing the "fiction" of the game, though. The day a new player buys the SCAG because "that's the setting for D&D" is the day D&D ceases to exist. They've created the Forgotten Realms RPG, which I have no interest in. If you're invited to a D&D game, it really shouldn't imply anything about the maps, NPCs, etc. There have always been fairly broad brush strokes about shared ecology, but that's about it.
I dunno. I'm really annoyed by it, right now. I thought the gray box was uninteresting, at best. Nothing in the last couple decades has improved the Realms. All the flavor bits (Drizzt, Harpers -- god gravy do I hate the Harpers --, RSE, Mystara, etc.) are like bubblegum and Skittles -- weirdly textured and disruptive of anything pleasant underneath. It's like trying to pick the flavor Blizzard you want and having the person behind the counter telling everyone asking "What size vanilla cone do you want?" Maybe they'll eventually burn away most of the Realms and I'll be fine with it. Honestly, I could probably use the SCAG, but only when divorced from the rest of Realms canon.