laikNo, not anyone could be the best. To be the best at something, it requires work + high cognitive abilities + possible natural aptitude. There are people who have entered Invite with sub 5k hours, and there are people with over 10k hours and little to show for it.
In lieu of any actual evidence, I'd argue that anyone with 10k hours who's not near the top of the player talent ladder probably didn't spend all 10k actually working at getting better. There would probably be a lot of time idle, casual or community pubs, surfing, playing easy jump maps, stuff like that. There's a genetic component to everything we do, but unless there's some sort of mental or physical handicap at play, I think anyone who spends 10k hours trying their best to get better would definitely find themselves at the top level.