I'm using Affinity v1 for some specific photo manipulation work, and the workflow is a bit convoluted.
Very tempting to make a specialized tool like this for that.
They were bought by Apple recently but still sell it. I moved to it when I migrated away from Photoshop. It doesn't have some of the fancier stuff like puppet mesh warp, but for an all-around editor I'd argue its unrivaled in the Mac space.
https://www.apple.com/pixelmator-pro
EDIT: Krita is also great (and free) but it feels more geared towards digital painting.
I'm glad to see entrants in this space!
It's really a shame the Paint.net author is so devoted to being Windows only.