There are champs that are broken and need to perpetually be 46-48% winrate. I would challenge the devs to buff a 1% pick/ban champ to 55%+ winrate and then leave it that way for a year, let me tell you what would happen, that champ (Let's call him Scrimblo) would start to get banned only by people who are hard countered by him, and people would also start to play champs that win hard against Scrimblo. So if say 'Dumby' hard counters Scrimblo, then you'll see 'Dumby's' pick rate go up. After one year people would shift their bans onto Scrimblo, and people would be playing champs that hard counter Scrimblo more often. So after one year Scrimblo would be 50% winrate with a 10% pick and 10% ban without any nerfs whatsoever.
This is just an educational example of how balance works, and that most champs who seem fine are actually completely busted.