The balance team is accountable to the company (they are Riot employees), and are forced from above to introduce changes that put certain champions in the limelight, or are ordered to not touch incredibly frustrating, problematic, long-standing broken, and recently released ludicrously overpowered champions because that would affect Riot's bottom line.
If a single person with some decision making leverage employed at their balance team had a backbone and acted on it, they would lose their job very quickly. Balance changes for the better go against profit motives, at least with the way the game is set up. Champions that aren't played sell no skins - why would they dare touch the mid lane cash cows a la Zed, Yasuo, Qiyana and more. I can't think of a recent champion release (ignoring long-standing garbage like Zed) where I had the thought Yep, I had a reasonable experience playing against this character.
This isn't even some insane redpill conspiracy theory. There is a depressing silence on Riot's side on every thread complaining about the recent (very often also recently released) fotm champion. Aphelios and Mordekaiser still get to run away with games even though we've established that they're too ludicrous to let people pick them. The 10.1 changes do nothing to address this. There is no 'strategy' or reasonable metagame around Ban Phase neither in solo queue or professional play. The latter has people target-ban champions against players consistently, and that's about it. If you are playing solo queue and aren't banning fotm champions (just look at the top 20 champion usage), you're probably running it down.
Of course Riot could start spewing PR crap (like the lutzburg puppet did) on every thread addressing the game's balance, but then the onus is on you to spot their lies and call them out for their bullshit, like this video response does.
On the other hand, the playtest team is some set of random nameless (!) players not affiliated with the company under NDA that have no teeth over what balance changes are implemented into the game.
What I want is some form of accountability. All balance changes should be discussed in a public forum, though only the people actually playtesting should have write access, where we can see what people are discussing, and balance changes should only ever consist of what discussions between Riot Games players and playtesters result in. That way we can call out Riot for obviously trying to milk their cash cows by ignoring discussions on those forums, and de-construct their spin, and remember and immortalize it for all eternity.
But that would never happen because in the end it still affects their bottom line negatively. It's a pipe dream.