I tried Gimp for a longer time, too, but I could not get used to the complicated layer management, missing layer effects & layer adjustment features. I will try out Affinity.

No version for Linux. Does it work under Wine?

Huge learning curve and a lot of missing features.

I have found most of the "high learning curve" is based more on work flow. Muscle memory can screw with you when trying to learn a new piece of software. I used to use Dreamweaver back in the day when I was on winblows, made the switch to Linux started using bluefish and had to change my work flow which was hard to learn because I was indoctrinated in the way dreamweaver worked. Actually had to relearn some aspects of web design since I had gotten used to the convenience of dreamweavers macros that were pre-installed

It's not an one-time purchase. I bought Affinity Photo for this purpose and then they released Affinity 2, and it wasn't a free upgrade for Affinity 1 owners.

I'm not buying Affinity 2 and buying every new release just like Parallels do. I'd rather stick with the old version or take a shot on Gimp instead.