Workflow is big, but it isn't the biggest issue with Gimp for serious work, the destructive editing is. Workflow you can get used to, destructive editing means you're fucked if you need to edit something you've previously edited - something most if not all professionals do all the time.

Not to mention that even if you personally managed to switch to something else, if you're not doing some completely solo work, you will still receive files from others (or may be expected to send files to others) in Adobe format. So even if you wouldn't be using it, you'd still have to pay for it to stay competitive. At which point you may as well use it because of what you said, that most of the alternatives are missing those expert features. So in professional setting, there's unfortunately no escaping Adobe. Someone would have to come up with an alternative feature full package of apps covering all bases (because Adobe isn't just Photoshop and not just graphic design but an entire interwoven ecosystem used in various related fields) and then work really, really hard to push the industry toward it. And it would still probably take a decade or two. So realistically, it would have to be or become some big corporation that would likely turn evil too as the time goes. Or some open source miracle like Blender that would have to attract enough big sponsors.

Not defending Adobe, just saying how it is. I have enough grievances about their software (how they managed to fuck up something as simple as Acrobat is beyond me) but you just have to deal with it or look for a job in another field. (I'm lucky enough that Adobe is only secondary software for me but even then I still can't escape it.)