So what you're saying is that balance should be dictated by using Bronze/Silver/Gold's lack of skill at using a champion as a guide? If a champion is played by a "very good Azir" and he does well against players of the same skill level, then that champion is good. It's like saying that Warwick is overpowered and needs nerfed because a Gold Warwick main destroys fellow Golds.
Think of competitive Melee/Project M. Fox, in both games, is currently ranked in S tier (the best of the best). He's also one of the hardest characters to play effectively due to the requirement to waveshine, drill-shine, short-hop double lazer, and generally become frame perfect with him. If I bring a Brawl/Smash 4 player to an actual Melee tournament (not some casual scene), put the controller in his hands and tell him to "play Fox and win." I assure you that he is GOING to lose that tournament, 100%. Fox is top tier, but unskilled players can't play him. That doesn't mean that he needs buffs.
At the end of the day, League of Legends is a competitive game FIRST. A game designed to meet and cater to high skill levels will STILL be appealing to casuals (take Melee and Project M as an example of that). However, a game designed around the casual, or low-skill level players will not survive a competitive scene (take Brawl as an example). Riot usually does, and always SHOULD look to high elos to dictate balance.
There is also a GIGANTIC factor called the Placebo Effect. A while back, Kennen's Mark of the Storm got a tooltip fix. For years his tooltip indicated that his passive stunned for one second; for years it was stunning people for an INTENDED 1.25 seconds. Riot finally noticed that this age-old buff wasn't reflected in his ability description, so they fixed it. Soon after, his winrate and popularity went up. Not because he got a buff, but because people BELIEVED that he was a better champion (other than a rare and minor glitch being fixed on his ult, he wasn't). The same goes for the LCS. When people play Varus in the LCS, people play him in normals and ranked, believe he is better, and play better because of that. However, when the meta moves on and away from Varus, people stop seeing him in the LCS, feel like there is a balance reason (it's really just the metagame, or "changing game"), and stop playing him DESPITE the fact that Riot buffed him in preseason.
Just give Azir time. The meta will favor him once again, and his winrate will go up once again.