Qt supports multiple backends for its own rendering, but the hobbyists will still have to rewrite their rendering code to support that new backend. For a lot of my programs, that's about equivalent to rewriting in another language.

Not when the hobbyists took the right approach to use the Qt 3D APIs, like the new scene graph API.

Also there is no harm in learning to write modular graphics engines with multiple backends, hobbits get to learn how professionals do it.

Finally, if it is just a hobby, then what hobbyists can do best to improve productivity is to use whatever their OS offers out of the box.

I got a small kick out of the typo, with hobbits learning to write graphics engines. No doubt between second breakfast and elevensies

Yeah, my English went downhill with auto-correction keyboards. :)