Instead of designing champs to be easy to play...
... how about make them complex but easy to understand instead?
I've read this line again and again when it comes to champions like Garen, Annie or Yi: "This is a champion new players like and can easily pick up, so we're not gonna change much or make them mechanically complex". However, since the game is balanced around the maxime that every champion has at least a minimum viability (unless you are kicked out to rott like Yorick), skilled players can abuse these easy-to-play and forgiving champs to gain an edge over those who actually bother to master a complex champion.
On top of that, playing the noob champs isn't much fun either, because you never really have a feeling of accomplishment.
Some time ago a friend of mine when he started league was completly turned off by the designs of (old) Ashe, Garen, Annie and so on - and even if he won games he asked me if there wasn't a "REAL" champ he could play. I told him to just experiment with the free week rotation.
Only a day later he found his new favourite champ: Syndra.
Sure, her difficulty rating is one of the highest in the game according to the champ profile, but her kit is just super easy to understand: make ball, throw ball, kick ball, ALL THE BALLS. Even the biggest noob can identify what this kit does and how it works after a few games - all that's left is simple practice and mechanics training. Sure, early on you're gonna make a lot of mistakes, but that's why you're practicing in the first place, no?
His second champ he fell in love with with Orianna, again because despite being easy to understand she had a really high skill ceiling that he could spend time trying to reach and feeling good when he actually managed to pull of some awesome play.
Old "noob champs" shouldn't exist in this current form in the first place, especially when the moment items and meta favour their rather simplistic playstyle they become downright atrocious to deal with (Hello Yi...). Instead, it's just enough when we have a bunch of champions that are just really easy to understand, but hard to master.
Mostly because if a champions kit is easy to understand, you can only blame yourself for failing something. It's kinda like DarkSouls. It's not the game's fault I misread an attack pattern I have seen ten times before, rolled myself into a wall because I was not aware of my surroundings or ran into a room Leeroy Jenkins style right into an ambush instead of carefully sneaking in with my guard up. It's all a failure on my account that I can use to improve myself by learning from it - and that's what gaming is pretty much about: to become better and better at something until you ultimatively master it.
Also, a certain minimum of champion complexity just equals a way more fun experience. What champ do you feel more proud to carry a game with? Tryndramere or Illaoi? Orianna or Annie? Ashe or Miss Fortune? Sion or Malphite? Usually the player tends to be more pleased with themselves the more complex the champion is. Everyone with two braincells can execute Garen's killing combo - but masterly preparing a multiple-ball-ult as Syndra, murdering the enemy squishy and then stun the enitre enemy team with a barrage of Dark Spheres? Now THAT'S something to be proud of!
Of course you can take the complexity too far to a point where it threatens game balance, but a certain minimum of complexity is required for good design in my eyes.
Tl, dr: Abolish the concept of "noob champs" - make easy to understand champs instead.