And I think even a human would struggle winning the character select mini game just with tabular data related to the players' win rates with those characters in previous matches. Learning about actual play styles of each playerand customising their play style with a given character would be a huge factor in them gaining an edge.
For example, let's say there is a player picking a slow but tanky character, but I happen to know the player who picked it often attempts a certain cheeky move to gain an advantage (like jungling early in the case of LoL, I really don't know much about Dota or LoL so you'll have to work with the metaphor here) and THAT cheeky technique is what increases their win rate. But then I know of a move that can be done by a certain character only in that specific cheeky scenario that will tip the scales and let me get a kill on them early, tipping the entire balance of the game early. As a pro player, that could be why I win with my selection, but the cheeky strategy also why the other guy often wins with his, even against other players who pick mine.
There's essentially a list of known play styles between different characters and optimal strategies to use with them against certain other characters. I think when you filtered to the top 10% of players, you essentiallly made sure a larger percent of those optimal play styles were the ones that generated the outcome data.
But still, if the player doesn't know what those in game strategies are, or their opponent doesnt know the ones they're "supposed" to be using, it'll throw off the value of making it the best selection.