Every SCOTUS Justice, except for for Thomas, was an absolute top-tier jurist at the time they were appointed.
Every SCOTUS Justice, except Thomas, could have received a tenured professorship at any law school in the country, a partnership at any law firm in the country, editorship of almost any law journal in the country, etc.
Any one, including Thomas, would have been welcome as a professor at the Unversities of Oxford, Cambridge, Edinburgh, Sydney, etc; a magic circle UK law firm; or as arbiter in international trade.
Any one, including Thomas, would have been a shoe in for attorney general or solicited general of US. Any one, including Thomas, could have gotten a position as US Attorney in either a Democratic or Republican administration.
We have an insanely well qualified SCOTUS, mostly because of how arduous the confirmation process is.