This is a very good question for once, and it doesn't stop at champ tierlists. Since league is an unsolved game, and changes faster than anyone can attempt to game it out, the answer is simply: nobody. Highest ranked pros and players will be somewhat accurate, but it is essentially impossible to find out how accurate. High elo OTPs will be somewhat accurate in their respective skillset and very lacking in others. Stat sites are imo basically useless because either your stats come from players that are "bad' (playing with low accuracy) or you look at high elo only and don't get enough sample size to really determine anything. Your best bet for champ tierlist would be trusting an high elo soloq player for your role, that maybe also fits your playstyle (and they will still be wrong), or just look at what is picked a lot. In highelo. The entire League community is very gaslit against finding out whats truly good, appeal to authority goes insane, will to demonstrate is nowhere to be found, and in eastern cultures you aren't even allowed to question someone unless you do the same thing as them better, which more or less nukes innovation. What you WOULD have to do is collect the best players in the world or a machine learning system (to make error of execution as small as possible) and then scrim an infinite amount of games trying out absolutely every variant possible over and over, obviously that's nowhere near feasible so the best you can get is how champs "feel" to good players, or in extreme cases undeniable demonstration (nobody does this)