Sorry if I miss a point made in a previous comment, I did my best to read most of it and gather how the conversation is flowing.
Now, I feel a huge problem with this conversation is defining "Simple". We can have (what I consider) "simple" champions in terms of mechanics (e.g. Sona, Udyr, old Soraka, Sion, Malph). We also have (again, what I consider) "simple" champions in terms of how to play them (e.g. Annie, Amumu, Caitlyn, Irelia) because even if the mechanics are not so simple they remain mostly a "straight forward" champion once you learn how to play them. You can also have a "simple" champion from the perspective of their roles (e.g. Morgana is quite easier to play as a mid laner than as a support IMO; you have to micro manage your cd's way more effectively to have an impact as a support).
So I guess the contribution I'm trying to make here is to state not only your "simple" champion example but also to explain a little bit on why or how you define it as simple. If you ask me Rammus is a simple champion in terms of mechanics, but if you truly want to be effective for your team, even knowing when to select him is as complex as it goes. Even in the proper team comp, he is also very situational when it comes to team fights. Do you want to CC the adc to abuse your W and Thronmail combo? or, do you want to remove that mid laner who can 1v4 the rest of your team?
I know this is a short example (and I love baby
) but lets go and give more insight in our comments ;)