Win rates dont matter in the sense that you shouldnt place too much stock in them. For example a champion with a low playrate but a high winrate isnt necessarily better than a champion with a high playrate and low winrate, and vice versa. It also depends on what elo youre playing at.

Does win rate affect MMR LOL?

Win-rate doesnt affect matchmaking. If win rate affects mmr, then it affects matchmaking. Matchmaking is done based off of MMR.It puts people with similar MMR up against each other. MMR however is mostly decided by your winrate, if your winrate is bad so will your MMR and youll get matched with absolute degenerates.