I don't think theres a general answer to this, it kinda depends on the respective champions and what Elo you take the winrates from.
Since there are champions whose strength are very different depending on the Elo they are played in. Azir in his prime for example still had a sub 50% Winrate on sites like champion.gg (which takes Plat+ games for its data) but was basically 100% Pick/Ban in competetive and high Elo (Master/Challenger) because if played right he was just so extremely strong.
Another example would be the current Ryze; champion.gg has him at the second lowest winrate in mid (43.96%, just above Azir) yet he still will get nerfed next patch for he is still an extremely strong champion when played right.
On the other hand, high winrates don't necessarily mean, a champion is too strong. Highest winrate Midlane Champion right now is Galio with 56.93%. But that basically just comes from the facts that 1.) nobody besides the super die-hard Galio Mains play him (0,75% Playrate) and 2.) nobody actually knows how to play against him. So the ones playing him know their champ and how to play him extremely well while their opponents probably haven't played against a Galio in ages and are making mistakes that the experienced Galio player can easily exploit.
And then there are also champions that have a high winrate AND high play-rate but have their winrates due to the natures of their kit. Janna would be an example, that has the highest winrate for Support for years despite beeing nerfed several times. That just comes from her kit; she's not too difficult to play and quite easy to pick up and she's basically super safe. Most games in Solo-Q are lost because someone feeds and the enemy snowballs the games. A decent Janna reduces the chance of their botlane feeding quite a lot due to the tools she has to safe her ADC from dieing. She most often doesn't win the botlane, but doesn't lose it either. And then she becomes a very good Teamfighting champion, especially against the many Assassins that are played quite a lot in Solo-Q. Janna is the ultimate cockblocker for Assassins; you try to get in, get ulted out. You try to get in again, nope, Tornado. You somehow finally get to a target? Exhausted. Still trying? Target shielded by her E, Locket, healed by redemption.
So, Janna with her current kit will probably always be a strong support in Solo-Q, unless they completely gut her numbers or rework parts of her kit.