I'm going to reiterate, while I don't think Garen needs to be a complex champion he should have some agency and strategic depth in his playstyle. He doesn't have that now, and because of this he is kept at a consistently weak state. Garen is a mess, and new players aren't going to learn good things with him. What they will learn is that this champion they spent a bunch of time practicing on is worthless when they improve, and that will be disheartening. It's not encouraging to commit to learning a champion you find fun and then realize that they are awful in any decent level of play.
Learner champions obviously need to have low skill floors, but the issue with Garen is that his skill cap isn't much higher. Master Yi, for example, isn't a particularly challenging champion to pick up and play. He does most of his damage through basic attacks, has no skill shots, an enemy targeted blink, a self heal, and two steroids. While his kit is simple, it still provides tactical depth. If you've ever seen Cowsep you know what Yi is capable of. Q can be used to dodge attacks and avoid damage, evade crowd control, and even drop turret agro. W can be used as an auto attack reset, and you can activate it and immediately cancel it to mitigate burst damage. Ashe is similar. Her kit is simple, she has a passive slow on her basic attacks, a basic attack enhancing steroid on Q, a multi-projectile cone skill shot on W, a global scouting tool on E, and a global skill shot stun on R. None of her abilities have complex interactions, but she has the potential to influence team fights with strong picks and is an exceptional duelist if her R is available.
I don't think anyone here would say that we need to dumb down Yi or Ashe; they're pretty fine as they are. I'm not saying we should turn Garen into Azir, but with how little he's capable of I hope he can get some work done to make him decent in the hands of and against a skilled player.