I feel like everybody is missing the point here.
True. With enough work, it's possible to beat any app into something usable. Back before the Mac, that's what we all had to do. It sucked. The reason Apple has been so successful over the years is that they have Human Interface Guidelines, so us users don't have to learn how to do the same exact thing in every new app. Open is always command-O. New is always command-N. Everybody is better off because of standardization.
You don't sell a car with the brake pedal in the glovebox, and then tell customers they can get the wrench out of the trunk if they want to change it.
Well, I'm not a Photoshop user, but Affinity Designer is more like Adobe Illustrator, and command-M is not "Curves" in Illustrator.
It's also not an Adobe product, at all, so I'm not sure why this is relevant. Is it trying to be a good Photoshop clone, or a good Mac application? There's gobs of other Photoshop keyboard shortcuts that it doesn't support at all. Instead of "F" to go full-screen, Affinity Designer uses the Mac standard command-control-F. That's a good thing!
Again, not sure why you're bringing this up. Nobody ever questioned that it was a conscious decision. Clearly, keyboard shortcuts don't just get assigned on accident.
I stated that it was (1) non-standard, (2) frustrating, and (3) unnecessary. I never said it was an accident. It's your application, and it's your prerogative to make the app behave weirdly if you want, but I think you're underestimating how much this is hurting your users.
Since apparently the Photoshop converts love customization so much, why not use the Mac standards as the default, and have a set of "Photoshop" keybindings that Photoshop people can use? Or at least go the other way, and give us a set of "Mac" keybindings? I really don't want to have to dig through all these keybindings to make it work like a normal app. Especially since half the keybindings just show up as the question-mark-in-a-box that's used for missing characters -- apparently nobody bothered to test this feature!