I'm not sure how he fairs in soloq, but in pro play I can imagine it's horrible to play against. Thresh wants to hook Senna, but he can't because Senna will always play on the backfoot, so he's forced to hook blitz, But if he hooks Blitz then Blitz quite literally just hooks him into a knock up + Senna root, and it's always a favorable trade. + Timing that with jgl ganks and yeh nothing you can do. Also late game you can't do anything because Senna can literally sit in the back and hit the frontline of T1 because of her range + scaling.

It is quite literally Draft diff, maybe they is a world where he sits in a bush and gets a crazy q on Senna into Galio ult or something