I have used Photosohop for almost 20 years, and then Affinity, Krita, and Gimp here and there. In my opinion, it's a bit of both. At first I thought I was just used to Photoshop and I had to just accept losing productivity to make the switch. But there something about Gimp UX that I can't get over, even though I can't really explain what is it. Of course fighting the muscle memory for all the features is a pain, but there's more. I can't find logic in the shortcuts, the menu organisation... I have not struggled as much for Krita or Affinity when I tried it.