Two ways of looking at that imo.
Based on natural talent, you are probably about right. Players like Jimmy White, Mark Williams, Judd Trump have all achieved less than Mark, but all of them play with a natural swagger.
Selby would be the first to tell you he has had to work hard at the game.
Based on an all-round game and tournament success I would put him about 5th.
Like John Higgins, he is a brutally tough match player, that is very difficult to beat particularly over longer distances.
Mark Selby should be a Leicester legend, I sometimes think he doesn't get as much appreciation for his success. I can say for a lad from New Parks, who at the age of 11 looked and dressed like a working class boy when I first met him, I am proud of what he has gone on to achieve. And better still he has always remained very grounded whenever we have met him back on the pool circuit. Credit to the lad