54-55%??
So you consider balanced to be having a greater chance of winning the game?
That is completely illogical.
For every win there is an equal loss. So for a champ to end up with a 54% winrate means others are losing. There is absolutely no semblance of balance in that idea. You could have a 45% winrate champ.
Wins do not come from nothing.
Let's do a little math experiment. You made a game with 10 champions. You got in 1,000,000 games with each of them. These games are 5v5 so there is still 1,000,000 in total. For the sake of argument we can assume the exact same person played the same champ each game so they have considerable experience. A mastery beyond any League player.
So if these champs need to have a 54% win rate to be balanced that means all of them must win 540,000 games each. Yet for all of them to win that much there would need to be 1,080,000 games in total which is 80,000 more than were actually played which is not possible.
Okay, so there is no way to give them all 54% so what if just someone has 54%? Well that means the other has 46% win rate just to maintain the first one's 54% win rate.
This is obviously not balance. Balance means the chances are equal. That no champion has a higher chance of winning than any other.
For there to be a higher chance of winning there has to be other factors such as imbalance, or playing against weaker players etc.
Now that we covered how that math of a 54-55% "balance" is entirely flawed let's move on to one final point. Win rate isn't actually an indicator of champion balance. There are far too many other factors that have nothing to do with the champs that affect win rates. They could help see balance within certain states/demographic but by themselves the win rate is circumstantial.