I think there are a few problems of perception in the larger tf2 community that lead to a lot of these near-uncoachable people.
There's the whole meme thing, which, whatever, we can't do anything about that. Then there are the people who are the same people on r/truetf2 who make threads like "HELP I ALREADY HAVE 70 HRS ON SCOUT AND I DON'T FEEL LIKE A GREAT PLAYER YET WHAT AM I DOING WRONG". We need to stress that, even as a newbie, it's probably better to have a basic level of competence in tf2 before starting comp tf2. Then there's the hardware/game customization stuff, it's really important that we make tutorials and the like about that as well so people know that someone with 10 fps prolly won't be amazing at this game. Finally, I think there's a serious problem where we liken being new to tf2 with being childlike and we coddle people too much. If the person I'm coaching is like 18+, I'm not going to treat him like an unruly 6 year old. I expect a certain level of maturity from people who aren't like 12, regardless of how long they've spent clicking polygons.