Absolutely it is successful. But the original goal of Linux was to create a personal free OS that had feature parity with Unix. It wasn't solving a previously

Absolutely it is successful. But the original goal of Linux was to create a personal free OS that had feature parity with Unix. It wasn't solving a previously unsolved problem, because the requirements were already given by Unix. The stage of software that benefits the most from close collaboration defining the requirements in the first place. That's very hard to do in isolation, unless the requirement is trivial/obvious. No doubt, later on, Linux developers came up with innovative new-to-the-world features for the OS, but a lot of these were developed by collaborative institutions like universities, companies, and governments.