It is the old comparing eras argument.
I believe that great players of the past would be great players now they would have adapted their games to modern conditions.
Being a champion is something ingrained inside you i think.
Davis v Selby would have been an interesting match though and probably a close match at that.
But if all the great players like Reardon, Davis, Hendry, O'S had all played at their peaks at the same time none of them would have been able to win as many world titles as they did.