Does skill based matchmaking actually exist, or is it a lie?

in don't think it exists in casual games, some times i can see from the drop that half of the lobby are preds and diamons, or soemtime i play agnist so many low levels that i get a great win, and i'm a medicore player. on ranked its another story, i feel it's more compatative even the match itself feels more fair (for me at least) so i'm more ready to accept a win or loss.