Yorick's winrate is absurd when he's mastered.

Cus he is so boring game wise anyone that still plays him deserves to win...

Everyone thinks he is complete shit, but he is in a good spot with item changed, and the Meta shifting.

Yorick is actually a lot like Urgot. They have pretty glaring weaknesses that aren't hard to take advantage of (even completely by accident). But once you overcome those weaknesses, they're actually ridiculously powerful in lane.

a lot of champions have high win rates when you've mastered them

Yorick really isn't one of the weakest champ in the game, many just believe that because of the sterotype but the reason yorick has such a low pick rate and win rate at the start is because if you fall behind u do nothing all game, but eventually you learn that you are one of the biggest lane bullies in game and can oppress the enemy top laner causing them to become useless all game.