anderDm can carry you, brains cant
This is 100% untrue, there are plenty of players who were on top teams with acceptable or even subpar dm who were smart.
Despite this, improving mechanics is something that you can do pretty easily up to a point and its also something you will have over a lot of other people if you play medic (people will love you and want to pick you up on teams if you can hit arrows and good surfs).