Champion screen includes PI after saga boost which isn't reflected in your profile. Okoye is higher prestige than Bastion which is probably why she appears above him.
The game characters have hidden parameter called prestige. It doesn't affect any gameplay directly, but can affect rewards in some game modes. The number you see is the result of some combination of that prestige thing and the masteries you're running. You can also use some sites to see how that prestige changes with sig, but overall the only thing you can say for sure is it increases with sig. Also I believe the increase with sig is not same for every champ, but I may be wrong, I've never seen any explanation from kabam on how it is calculated
Tldr: just see it as a random number
it’s not hidden, it’s the base hero rating in the filters . That is the prestige
Ahhh thanks for the info...