According to League of Graphs

And I don't know how accurate this is, but the weakest champion after 50 games played is Lee Sin, at 49.9% winrate.

And at 60 games it passes 50%.

Why does this matter? Two reasons...or one in two parts.

1. There aren't really any bad champions, only bad players. And by bad I don't mean "Can't play league well", I mean "Makes an unpracticed pick in ranked." Stop harassing your teammates for out-of-meta champs, if they've put in the time it's a good pick.

2. Similarly, your best pick is almost always your most-played champion in the role. Rather than chasing the ever-changing meta, chose a few champions who's kit you enjoy, and learn them well. You'll do better.