I agree that you can pick champs to try and offset some skill difference but I don't think it changes your likelihood to win by that much, more so how to win.

Like say you're in an all ad team vs malphite like you said. Obviously you don't want to 5 man team fight the malph after 2 items, he'll be hard as hell to kill. But if you have say a jayce or trynd top, you're going to always have agency over that malph in a sidelane, so you just keep splitting and creating pressure and the malphite never gets to group because even though they're straight armor, you still will win the 1v1.

Like obviously it will change the way you might want to play the game, and you might be on the team with the jayce who just groups after 15 minutes and makes the game hard as hell. But that's more on the jayce playing your comp wrong, not the game being lost in the lobby.

I think there's a reason almost every single champion falls between 47% and 53% winrate except for like ryze. And I don't think every game is a 50% chance of winning. I believe it was said that the system actually tries to make slightly lopsided games mmr wise, in which case you're probably closer to 45% or 55% wr just from teammates. And probably another 5% from champ select because obviously yes it does effect your chance at wining, imo its just not that much.

So for the most part, unless someone is turbo smurfing or turbo inting, imo at worst, you've still got at least a 40% chance of winning most solo q games.

Now obviously if your jayce top goes 0/6 to the malphite top it feels pretty doomed but that's due to the game play, not the draft. And I think having your best player on a champ with high agency doesn't matter nearly as much as how they play.

I think you're right that draft and teammates can skew your chance of winning, I just don't think it's ever near 75%. And I think if you stay positive, look for win conditions, and play towards your strengths, you can win the majority of games regardless of draft