Maybe balancing the game for the 0.1% is not such a good idea

They already don't do that.

They constantly update the player base on how they balance the game, and currently it's "Good in a least one range (normal, high, elite, and/or pro play), and not broken in any". That means if something's broken in a specific elo range, they'll nerf it, and if something's straight trash in every elo range, they'll buff it.

To be fair, there's no "correct" answer to game balance.

Riot does their best, and that's all we can ask for, at the end of the day they're just a company trying to make decisions that they think are best with what information they have. How's it their fault if two players who spend literally their entire work day with each other come up with hairbrained ideas like Taric+Sona in the bot lane and find it works way better than expected.

You can't balance a game for the masses, because then people with natural talent, good insight, or a head for mechanics can look at your game and abuse the loopholes. One game that tries to do this is Paladins, when I used to play there were patches upon patches for the same character. Instead of waiting a few months to see if their changes were effective they would look solely at pick and win rates and say "This character must be OP. They're picked 30% of the time for their role and win 60% of those games. We need to nerf them." Then they'd gut the character, then a few weeks later they'd "Hotfix" the character back to being stronger than before.

On the other side you can't balance a game solely for the competitive scene otherwise you drive away the casual players. Riot used to balance around the competitive meta, and they still do to some extent. If a character is "the best choice" for a role according to the pros they nerf that character to force newcomers into the meta because who wants to watch the same 10 champions duke it out year after year at worlds?

It's not as bad today as it was the in past though, there are still champions that go unnerfed despite the lower ranked players claiming their OP (Blitz in Silver down for example) but in higher ELOs you don't even hear that character get mentioned, and there are still champs that dominate the higher ELOs, but nine times out of ten those champs have incredibly high skill ceilings that you're required to be at to make them viable at that level of play.

TL;DR You can't balance a game for everyone, there will always be "something wrong". No game in history has ever made a "perfect roster" so we can't expect Riot to do so while also keeping the game in a constant state of evolution.

why would they balance the game around people who aren't good at the game (implying they do this of course)