FFXIV stands out as a modern game that handles audio devices as if it was created in the 80s/90s/very very early 2000s... It locks onto the default windows audio device upon starting and will not change afterwards without restarting the game (which is kind of rediculous, forcing people to exit the game should be the last thing that you want...)

This has been an issue since 2.0 (or even 1.0 according to the one forum post). Here are some previous threads, all of which have been closed without the problem actually being addressed, there are other, plus several Reddit threads as well:
That last one actually has a moderator posting in 2014 saying that you were supposedly working with Microsoft trying to fix this issue. Well here we are over 4 years later and it's still not fixed.

FFXIV is an MMO, people want to be able to switch devices so they can join a voice chat, or starting a stream, or it's getting late so they want to make less noise to not disturb others, etc... Please, please, please use a little bit of the millions of dollars you make on this game and fix this very very basic issue...