This exact attitude is the entire reason why Riot thinks they're completely infallible with their decisions. There's always a few people who say "nobody on the boards could possibly be more correct about balance or design than the Riot teams are", and Riot takes that to mean "Welp, guess we never have to actually critically examine our decisions or mistakes".
Believe it or not, there are people who don't work at Riot who can perform basic math, reference gameplay experiences, provide analytical comparisons, and examine relations between the different mechanisms that bind together to make a champion. They don't have a monopoly on balance or design, and the fact they pretend it's some kind of elitist club where outside opinions are immediately less valid (and the fact that there are people who let them believe so) is a big issue with the balance and characters of League in general. At least in the past few years (once upon a time Riot was significantly more open to the thoughts of their community)
If large amounts of people complain about a champion for literally years (or as long as the champion has existed, for some of them) being unfair, there is a fundamental problem with that champion's design. That is just blatant fact. Champions should not cause an incredibly un-fun or unfair experience for the players who are playing against them, and any designer worth their salt would tell you that the player/opponent dynamic is a necessary consideration when introducing competitive elements to a game. Hell, Riot themselves have stated this exact same paradigm multiple times over.
The fact that they believe (or even they don't believe, their action support) it's okay to not critically examine or redesign characters who fail to create a fair experience for both sides of interactions with that character is both a problem and a failing by Riot as designers. Even more unfortunate is their stark refusal to accept that maybe a couple people working on a balance team saying "nahhhhhh X champ is fine" is not always more credible than extensive, mass opinions of many players who disagree. The "idiot masses" aren't always right by any means to be sure, but when it comes to Riot their actions when it comes to reworks and balancing seem to reflect they have the belief "We at Riot are the only ones brilliant and infallible enough to understand our own game", which is simply not true.
If a character is regularly complained about as being unfair by a large amount of players, in some cases for several years and in other cases as long as the character has been released, there is a problem with the character. No matter how many of that character's fans insist it's fine, or how much the developer blatantly favors them.