Except...... (I'm generally in agreement with the premise) Attractive champions just arbitrarily get more play than champions who are not.
Ezreal for example, has had MANY periods where he's a 47-48% win rate champion, but maintained a 30% adc pick rate simply because he was a) Noninteractive and people are getting filled adc and b) because people who are into pretty boys like him.
Akali still gets play after atrocious nerfs...... because the current version is absolutely gorgeous.
Kai Sai has seen atrocious nerfs but again..... is still a 12.75% pick rate adc.
Pyke fulfilled the "I'm a badass from the shadows" fantasy; he's been reworked into a dead spot, yet still maintains a 10% pick rate.
Anywho; the reason Riot is doing this:
They aren't looking at a stat/skill breakdown deep dive research of the champions they have created (their strengths, weaknesses, all given logs and dummy values to represent them in comparison to other champs to do analysis for balance.
Instead they are using arbitrary numbers like Ban rate and pick rates, which are heavily driven by player sentiment, opinions, sometimes aesthetics.
What this creates is situations where a champion like Zed, evolves into a front loaded assassin with relatively short cooldowns and energy gain, because his kit is generally used as a 1 target executioner, which leaves him windows to die, and the fact that players generally over-focus on killing with him leads to him not showing up statistically as a lane pusher. His single assassination and even aoe parity with Electrocute is monstrous. But it gets ignored in its strengths because his player built shortcomings have told Riot he's balanced, because players generally don't do everything they can with him.
Or a situation like Talon, where you're combating the urge to stay in lane versus roaming the entire game; Traditional mids stay mid and roam a little. Talon's job is to literally roam 95% of the game, and not actually lane except in passing. His kit when played correctly is oppressive to everyone he crosses path with, which is why he's been a top 10 champion for over 6 years. But..... riot is blinded to the fact part of the statistics around Talon are those players who just stay in lane and afk the game away waiting until 6 are weighing down his actual performance.
They're assuming that in cases like these, bulk games average out balance, when in game micro balance may be an entirely different story altogether.
Also, they're ignoring we're in a social media stage of game playing, and that fads occur which change long held consensus on some champions. Like what's happening with Sona/Soraka is HEAVILY being driven by social pressures and reddit feeds, not actual balance.
Riot also used to balance around entire champion average play, not single lane performance. Now, they feel that they need to average everything out per lane role, which is impossible.