50% win rate with a 40% play rate. The win rate seems respectable, but then you have to account for all the people that play him only occasionally/ are bad, which is a lot because of his high play rate. When looking at the statistics for dedicated players(players that play him often and well), its a 52.5% win rate on top of that he has a 5% higher win rate early-mid game, and only a 1% lower win rate late game. On top of all this he is ranked 2nd best jungler, and is pick or ban in pro play. [statistics from champion.gg]
I would also like to make my statement more concise, he isn't too strong in the sense "OMG NERF THIS GUY", its more like, he has a lot to his kit that feels like you can't do anything about, paired with his high skill ceiling and subsequent win rate to that high skill ceiling, he feels just a tad over powered.