It does not increase performance as in a higher framerates. It does however increase your minimum framerates (1% lows) in some scenarios. It is more a minimum effort tweak to decrease the risk of stutter.

I do. I just downloaded XIVLauncher from the discovery store in desktop mode, added it as a non steam app and then run it in game mode. It downloads FFXIV on its own and manages its own Wine prefix for it.