... and again the winrate argument.
Winrates doesn't mean crap. They are influenced by too many variables and the actual difference is 2% at best. Play rates, matchups, team compositions. That is something you can't see from winrate.
On top of that, despite mages doing poorly because they are still played on pro level players still believe they are in meta and so they are still picking them. If both team gets mage well one of them is going to win right? And then we can get to 50% winrate. Another reason for playing mages is that many midlaners just can't play anything else and mages aren't viable anywhere else (bot? get oneshoted the moment marksman returns with stormrazor, top? you can do 4 ability rotations and you won't get even close to killing that juggernaut/fighter which he murders you with one combo. Jungle? Slow clear, mána issues and innability to contest camps/scuttle.
Ahri specifically is rather assassin with mage patterns but without mage weaknesses and she got buffed and deals true damage which makes her solid pick. In other times players pick full squishy teamcomp and don't build mr (low elo) hence mages can actually do something and carry a game.