It's quite a bit different than prismatic crystal, frankly all it does is turn ST into 2 target which is something you *should* be really comfortable doing if you've any intention of playing aff.
While this was true in the past, the issue now is that you can't realistically have all 3 specs up to speed without tremendous luck and effort. It's not just a simple matter of AP, but relics and legendaries as well. My destruction weapon is 905 for instance, my aff weapon is 877, I have two destro berries and no aff one. Now I could have tried to split myself thin between the two specs, but that'd just mean I perform neither as well as I could have. This is also an issue because each individual spec isn't as far apart as they've been in the past, and any time that happens then the most well rounded spec becomes thee spec which you can't fix without homogenizing things which is something they're increasingly shying away from this xpac.
This xpac at least for now is very catered toward the type of player that identifies as an individual spec as opposed to a class. Which is where I imagine you find all the anger about individual specs like aff.
I'm not sure what glaring rotational issues exist. I don't enjoy playing demo at all, but there's nothing fundamentally wrong with it. It'd be perfectly fine staying this way for the rest of the xpac.
I imagine if we see any mechanical changes to demo it'll just be to make it more enjoyable to play, but not because there's anything truly wrong with it.
The only class that's beating me on mythic ursoc is our spriest, and spriests are absolutely broken right now due to surrender.