"Good enough" is highly subjective. You're entitled to your opinion, of course, but millions of people also think otherwise.
> Even as a business user, knowing that if I build an app and it probably won’t work in 5 years, is all I need to know about this hobbyist toy.
That ultimately depends on your tech stack and app features, much more than your OS. If you build a statically linked ELF binary that runs on the command line, chances are it will continue to work decades from now. If, OTOH, your app depends on a specific version of a GUI toolkit or some esoteric libraries, you might run into issues in the future. This is the same on any other OS. Microsoft does a commendable job at maintaining backwards compatibility for apps written in their supported stacks, but step outside of this and you'll experience problems. Same for macOS to a lesser extent (Carbon -> Cocoa, etc.).