It's not a completely outrageous point. There is a not-insignificant group of Apple customers who are using their Macs for design purposes with Photoshop being their primary tool.
If Photoshop ceased to be available on the Mac (or performed below standard) then which is more likely?
They find some other tool? Or switch to an Operating System which lets them run their tool of choice?
For casual photo editing, you would probably try a different tool. For professionals who live in Photoshop, they'll probably just switch to Windows.
If Photoshop ceased to exist for the Mac, that's a huge opportunity for a 3rd party developer or Apple themselves to fill the gap. While most Mac OS users can now simply boot into Windows, I'm sure they wouldn't all be happy about it.
Professional designers will switch to whatever platform Photoshop runs in. For many of them, the reason they run mac in the first place is because it has better support for their design tools.
If Photoshop ceased to be available on the Mac (or performed below standard) then which is more likely?
They find some other tool? Or switch to an Operating System which lets them run their tool of choice?
For casual photo editing, you would probably try a different tool. For professionals who live in Photoshop, they'll probably just switch to Windows.