It's a fruitless idea to balance around lower elo play because it innately, by design, harms balance at higher levels of play.

This is the crux of our disagreement I think.

I disagree quite strongly that this is a fundamental tension that can never be overcome. There are plenty of champions that see a lot of viable play at both Bronze and Challenger. Moreover, while (as I said) it's difficult to keep a champion relevant at all levels of play, if you're going to make a champion unplayable at one tier, it should generally be high-tier. Warwick is a great example: he's balanced in such a way that he largely isn't played in LCS, but he's great for new players. Even as someone who enjoys difficult champions, I think that's better than Lee Sin, who is consistently relevant in LCS, but essentially a trap for Bronze players.

And, crucially, I don't think many people feel like it's unfair or bad balancing when Warwick isn't viable in LCS. There's nothing wrong with that situation at all.

And there are countless examples of this design philosophy in other games. It's been discussed to death, usually in the guise of "first order optimal" choices. Warwick is LoL's noobtube and a well-designed noobtube is healthy for a game. Giving brand new players the option to use the most difficult gun in the game, which requires a ton of practice and a lot of game knowledge to use effectively, is problematic. It's especially problematic in heavily team-based games. This is why a lot of other competitive games use tiered unlocking systems for instance.

There is no inherent nobility to balancing around the competitive scene. It's no more entitled to ask for balance around less-skilled players than it is to ask for balance around high-level play (no one is saying we balance the game around Bronze 5 so let's stop throwing around the term "casual" like some sort of epithet).