Well, this isn't FPS. Higher rank shouldn't solely mean better mechanics. Players should be rewarded for learning strategy just as much as improving mechanically. You know Annie Bot, but there are also people who main Taric in high elo successfully. Low mechanical skill cap isn't a bad thing, nor is it harder to balance.
For example, most of the new champions/reworks were overtuned at release, and even after series of nerfs they were strong.
This means that they're harder to balance, not easier. They have a lot of stuff in their kits, and so nerfing one ability means that the champion might still be overpowered. On the other hand, Bard was very weak at release, both because people aren't used to playing him/with him, and because his numbers were undertuned. He got a bunch of buffs until he started seeing decent winrate. Still showing how complex champions are harder to balance.
Outplaying isn't just dashing around everywhere dodging skillshots and doing tons of burst damage. We're used to seeing outplay montage of Zed, Yasuo, Riven, Vayne, etc., but there's also CC, teamwork, positioning, etc. That's all outplaying.
For example, Annie can counterplay spell shields by holding onto her Pyromania stacks up to 3, popping spell shield with one ability then stunning the enemy with another. That's outplaying. A grouped up enemy following Amumu can be baited into his ultimate followed by a bad teamfight. That's outplaying. A low health Singed baiting the enemy to follow him is outplaying. And for all of these examples, they can do it even if they're behind.
A fed Riven/Yi/Katarina/Fiora noobstomping in 1v5 is technically outplaying, sure, but that's not the only kind of outplaying.
Anyway, back to balance. It's easier to balance an Annie than for example, Yasuo, because you can just nerf or buff Annie's problem ability. Maybe she's charging her stun too easily with her E? You can raise its CD or mana cost. Maybe her waveclear is too weak? You can buff her W damage. For Yasuo, it's a different story. After his Q cooldown became static 4 seconds instead of 5~4 seconds, that meant not only is it easier for Yasuo to charge his knockup, Yasuo players are now incentivized to put points into his other spells. Since he also gains CDR on his Q from his attack speed, that means that the developers also need to look at his itemization before buffing/nerfing him. Because his kit is more complex, it's more difficult to buff/nerf him correctly.