Hmmm your making me not want to swap now aha,I have both the rog swift and the x34a and I only game on the x34 , I couldn't go back either
For me its simple 4k = more detail and in some games it will shine better like single player RPGs where you stop and look.
Ultrawide is more immersion.
I have a 4k OLED Tv which I hooked up to play Destiny 2 and it was stunning but the slow refresh and boxed view killed it for me.
Playing Destiny 2 on a 49 or 34 Ultrawide is for me the best experience for the game.