What's coming out for D&D in 2017?
Tharizdun has been in the Realms since the 4th Edition era.
So... He was a new arrival, too. The Realmsification of D&D is older than just 5E, and it's always been a bad thing.
Strahd wasn't in the Realms. He was in Barovia, as always.
The adventure begins in the Realms for one cut scene, before the adventurers are snatched up by the Mists.
Which was stupid. There was no reason to have any reference
anywhere in CoS to
any other setting.
This should serve as a cardinal example of things to not do.
So, really, it's just Acererak.
I don't have a problem with an epic level demilich travelling between the planes. Especially after cheating death three or four times...
Meh... Really, it's the Realms. I don't know that I have a problem with a plane jumping demi-lich, either. Just stop going back to the Realms. It might be cute if they were supporting multiple settings and kind of swapping them around. But they aren't.
Actually, it's more about the monotony. D&D should be more about home brew worlds than published worlds.
First, keep core books and "generic" adventures devoid of anything more than random names with almost no context.
Second, no one setting should get more than, say, 1.5 times the attention of any other. If you have one setting that's substantively outselling second place, work intentionally to shift that.
Third, use language that encourages DMs to build their own world and tweak published settings.
I have extremely mixed feelings about 5E. On the one hand, they managed to have probably the mechanically best version of the rules, to date. On the other, the handling of settings and other fluff is easily the worst of any time's I have to assume that either different people are making decisions out the rules quality is sheer luck.
And, yes, I'll acknowledge a particular contempt for the Realms that goes back to the gray box. But, I'd still object if Greyhawk, Krynn, or any other setting was in its place.