Well there could be engine restrictions at work there. There may be a limit to how effectively they can phase the game terrain. Likewise there is issues with having multiple instanced versions of the same area as it can split up the player base. Id say the only time it would work ok is in situations like dungeons where the dungeon is the first time you see the location and after the dungeon it opens up in its aftermath state.

Personally I did find Alexander somewhat underwhelming and frankly the fact that he is about at least 4 or 5 times smaller in the game world than he would have to be for us to have the space we have inside the raid also kind of throws me off.

As for Primals, while Alex feels a bit underwhelming, I think Bismarck was certainly handled well and Thordan's fight was incredibly epic.