Yorick is only strong in lane, and since people who are actually good at the game can farm under tower (since yorick pushes waves) he isn't a problem.
Darius has a lot of level 1 and 2 damage, and a good level 6 spike...but he is very far from having a toxic kit.
Akali was literally just nerfed. If you are unfamiliar with WHY that is a big deal, then you've never played against a good akali. They took out her level 2 cheese.
Gangplank...is bad lol, he is so bad. Oh he crits you for a huge chunk? Well since that is he only damaging ability why don't you punish him every time he uses it -_-
Yorick hasn't been reworked because 1) no one plays him 2) he is actually easy to deal with out side of lane and his map pressure is minimal 3) His rework will have to still include ghouls since that is what identities him as a champion. That takes time to work out.
Note: I know Yorick is "strong" in lane, but much of his strength comes from people not knowing how to play against him. Anyone familiar with how Yorick works can have a pretty easy time in the laning phase. He is worthless without mana and all his poke has high mana costs. Kill him before his tear, or whenever he runs oom.