But it was one of the rallying cries against 4e--explicitly. People were really bent out of shape about it, and made a huge stink.
I should think there would be rather a big difference between, "We are using this system, which happens to share the absolute rock-bottom underlying mechanics, but only one particular splat" and "Well, we're actually using the exact same book as everyone else using this system, and most of the same contents, but I'm picking and choosing which ones in that book, and I refuse to ever even slightly entertain a moment's discussion about why I picked some and not others."
Perhaps not always--but it is very close to being so. Accommodation is almost always possible, so long as everyone is willing to make, and work with, good-faith discussion and compromise. (I repeat, everyone, all persons, each individual participant, every player and every DM, genuinely actually all sapient intelligences involved, hopefully that's specific enough so that I won't be told yet again that I'm somehow only talking about DMs when I say that even though I've literally never said anything other than "everybody needs to play ball" and "nobody gets a free pass.")