I would agree a few years ago, but saying that it's generally not usable for users is (in my opinion) wrong. If you're only going to use a browser, and watch some videos, Linux is fine. If you're a gamer and only use Steam, Linux is fine. Linux was also fine for me when installing Lutris to run other Windows games like Trackmania. For both those cases, I didn't even have to touch the command line. If you're a programmer, Linux is probably fine, because you have more knowledge on how command lines work anyways.

If you have any kind of advanced use case that doesn't have a well established solution, and you have to research (sometimes a little, sometimes a lot), that's probably not fine for a normal user. But more and more tools do have established solutions that work out of the box, so I'd say it's getting more fine.

Whether Windows, Mac or Linux is better is a question of use case and other factors in my opinion. You only used Windows your whole life and don't want to get used to a new thing? Then don't. You love the Apple ecosystem and want to pay the premium? Do so. But I feel like outright saying Linux isn't for regular use has become false in the recent years, as there are quite a few use cases by now that can use Linux without problems.