I'm A Banana
Potassium-Rich
pemerton said:Why can't the Dark Sun player just ignore that new baggage, just as I might have to ignore Planescape baggage to use mezzodaemons in the ways that I want to?
It's not a question of capability, it's a question of the game easily facilitating the kind of game you like to play or not.
If mezzoloths were defined in 5e as, I dunno, mutant scarab-people who dwelt in the deserts of the material world (in other words, something they've never been), you'd hit a bit of a barrier when you go to use them for your purposes as 4e demons. A barrier that, conveniently enough, 4e doesn't hit. If mezzoloths are part of the core of your game, something your players and you have used and have expectations about, possessing the 4e fiction that's important to your games, 5e suddenly doesn't look like a purchase that's going to help your games out much. Better off to stick with the lifetime supply of adventure that 4e already offers, since at least you don't have to edit every appearance of a mezzoloth in your game.
It's not giving you the tools that help you tell that story. Sure, you're capable of ignoring it....if 5e offers other stuff you like, maybe you will. But the more it changes, the more it invalidates your previous game, the more trouble it is to convert, the more likely you are just to never buy 5e, and just keep going with 4e.
Mezzoloths in 5e should enable you to tell the stories you've already been telling with them. They can be multivalent -- capable of being used in many different stories -- but they should retain their utility as the same kind of tools they've been used as before.