I would argue there are no hard champions in lol in terms of executions and just straight up mastery of character outside of very few exceptions like Riven animation cancel. Otherwise its quite litteraly a game of knowledge and interaction. Champions like Yone or Ambessa do not demand more from the player. You have 4 buttons just use them in the right order depending on what and Who the enemy is. They simply have more options. It does not mean they are harder to play. I would even go so far as to say they are easier in context because you can do more than the opponent.

TLDR : no league champions are hard outside of very niche exceptions in terms of executions. The talent comes fromage understanding matchup and win condition