I suspect that most, even a lot of professional users, could get along just fine with CS1 or CS2. The core functionality hasn’t changed all that much and in a lot of ways, CS/CC apps have gotten worse. The only reason these individuals aren't still using those old versions is because they aren’t well suited for modern machines.

I’d personally be elated if Adobe started selling a lightly modernized single-purchase Photoshop CS1, even if it cost what single purchase PS licenses used to. The lack of cruft and UI churn alone would be worth it before even getting into the savings compared to a subscription.

There are no other workflows that 100% match Adobe Photoshop. Until you like-for-like replicate the workflow, professionals will continue to use PS.