What is considered an acceptable win rate? And what are the factors you have to account for?

This one has been bothering me for a while. Depending on who you ask, you get a different answer. A lot of this comes down to each players style and how they think the game should play. Is a champion "balanced" if they have a 60% win rate, BUT only in games that go to 40 mins or longer? What if that champion had a 30% win rate in games that ended around the 20 min mark? Is a champion "too weak" with a 47-48% win rate, but a 30-35% play rate for their role? Is a champion "too good" if they manage an average of 54% win rate BUT only have a 1-2% play rate for their role?

Clearly their will be champions that thrive at different points in the game. But the question remains, how "good" is a champion allowed to be if they have a "bad" point in the game? How much does the meta effect those numbers? Clearly in a meta where champions are some combo of tanky and very self healing, a champion that needs to do constant chip damage to win, is going to have very bad numbers. In an engage meta is considered strong. If the meta is the only thing that changed, does need to be nerfed because her win rate at all points of the game is now 53-54% with something like a 20% play rate? Or is she fine, since her % was something around 49-50% before the meta shift?

Another thing to consider is how "hard" the character is to play. Can an "easy" champion be allowed to average a high win rate? How high or low can a champions win/loss % go based on difficulty of playing the character? Is a champion who averages a 38% win rate with players just picking them up, too weak even if that champion averages a 52.5% win rate with players what have played them in dozens of games? How do you "balance" a champion with a 56% win rate in pro play but only a 44% win rate in Solo Q? What about the opposite, a champion that dominates in Solo Q where few people understand how they work, but is considered garbage tier in pro play since everyone knows their weaknesses and how to exploit them.

I personally think that some characters, like say , are in a bad spot because they have points in the game where they are so weak that they are an actual burden on their team... BUT also have points where they are monsters to fight against, thus ending with an average win rate around 51-53% which most people would argue is good - maybe a bit strong.