Don't look at the effort. Look at the final result. Lolita took all of four months to write, and it's terrific. That's less time than it took Ed Wood to make any of his movies, all of which bombed.
Are you sure Nabokov didn't think about the issues that led to writing Lolita in the years before he started putting words on paper? Maybe he really did put in more effort (e.g., in writing other novels) before Lolita was such a result in such a seemingly short time. Nabokov's autobiography suggests he worked hard for a long time developing his craft.
I think whether he spent 10 years on it or 15 minutes doesn't really matter, the work stands on its own, it is a creation. Sports as such - especially top sports where the 1/100th of a second counter makes the difference - does not create anything of inherent value.
The guinness book of records might make you believe otherwise, but it really does not matter who ran a little faster than his fellow humans.
Without Nabokov, Bach or van Gogh though, we'd all be a little poorer.
