We have sometimes missed this thread topic, yes. I don't think a failure to properly enforce this in the past is reason to let it slide currently, however, especially when requests to fire the balance team are pretty much always a worse replacement for threads that actually detail an individual's problems with the current game.
It's not a matter of "missed some in the past", it's a matter of "was not applied that way in the past." Which again raises the question of when that change in moderation happened.
In short, demanding someone's job over a design decision that you disagree with is a jerk move
It's an expression of frustration that no one expects to be taken literally. You wouldn't take down a post with the f-word in the title for "mature content", because you know the word wasn't meant literally. Same thing here.
not something Riot will take action on,
We both know that the odds of Riot taking action based on a single thread are slim to none. It doesn't matter how well written your thread is, Riot won't take action on it and it alone. It took how many threads complaining about how out of hand damage was for Riot to say they'd start investigating it? Are you telling me there were zero well written threads about damage creep before then?
and the thread that occupies a place that could be occupied with a more productive thread discussing your specific issues
We're not talking disk space (Riot would just clean up old threads if that was the case) so you must be talking about front page space.
If it's even occupying front page space it's because people either agree with the general sentiment expressed, or they're discussing it in the comments and expanding on what the OP started - or debunking it. Either outcome means that the Community feels it's worth talking about.
in a way that Riot could read and add to their data.
What even is this statement? You're not daring to suggest that Riot balances based on the number of posts, are you?