Azir and Yasuo are the only mechanically intensive champions in this game and it's not even close

Now hear me out, no real champion actually takes skill in this game (hell Electrocute makes half of roster look facerolly AF), it's all about your mechanics and decision making. If you make the correct decision more than 50% of the time, you should have no problem reaching Diamond. But when it comes to correctly accordingly controling your character, Azir and Yasuo are the hardest.

Everything about screams "carry and control". A successfull 5 man Emperor's Divide is extremely hard to land and it's totally game changing. Azir players are scary. Good Azir players are terrifying and are complete X-factor in the game and can carry the match 1v9.

however is extremely hated because let's admit it, even when champs kitwise are reworked to match him, he is still a force to be reckoned with, the possibilities when playing Yasuo are endless and so does the ability to fuck up. Squishy characters are usually far harder to play than tanks and Yasuo is anything but tanky. It's a champion that's vulnerable to ganks, has no real escape besides the enemy minions. Basically playing Yasuo successfully requires you to constantly outplay the enemy team and playing him to full potential requires extreme finesse and decision making. Yasuo is anything but reliable, however you could argue about it when he has a on his team. The point stands that playing this character solo and when behind is extremely hard.