Lemme start with saying I partially agree with you. BUT:
Making Teemo less "annoying" also means "not an early game lane bully", which is something Riot seems to be removing from the game, because I guess denying hypercarries the ability to reach their 'late game fantasy' is somehow bad.
They have my tacit disapproval.
And I actually do think it's ok to change champions so they're not as frustrating to play against. Think about it this way: Hypothetical current champion makes it so his lane opponent can do next to nothing in lane, not through smart play but just a toxic kit. Is it ok for this one player to say "no you can't have fun this game" just because of his champion choice?
This example is hypothetical because barring an extremely unlikely or specific kit interaction, this doesn't exist in league, and even so, if it exists for only a small number of the possible 15800+ lane match ups (yes, there are that many), it's still fine, and destroying the kit of a champion people already enjoy for other people is simply bad customer service. It implies the opinion of people who don't care about the content you enjoy is more important than yours, someone who enjoys said content.
There are two sides to this. The onnus is on Riot to not release a champion who interacts in this way to begin with, if they don't, people can't grow attached to the champion. They have to produce a good product. It's like, literally their job.
And to their credit, (with the noted exception of Kalista -_-;) I can't think of a champion that's been released with a kit that operates this way since like, the original 40, and again to their credit, they have been trying to gradually move away from that sort of problem without completely destroying the kits of said champions.
I am not a fan of reworks, especially not reworks made to benefit people other than the people who play the champion being reworked. Some are good, Ashe's was good, for example. Some are awful. Zilean comes to mind. Some completely delete the champion people loved and replace them, which is sad. Karma fans are STILL upset.
Here's my hypothetical; say you main and love a champion who is unpopular. Someone like Shaco, who I main. You know they're not exactly the least frustrating, but you love them, you love how they play, you love their aesthetic.
Now imagine the boards start circlejerking about how your champion needs a rework, you know that other than being annoying your champion is fine. In Shaco's case the only true anti-pattern in his kit is his passive, which isn't usually what people are annoyed by anyway. But your favourite champion gets queued up to be completely destroyed, your fun is taken away, and it's done so on the altar of the fun of people who never cared about Shaco.
How does that feel as a customer/player?