Twiggy-Snip-
I would probably fall into the "played for a while and still slightly below average" category but let me clarify. I'm not saying I don't want to play with beginners, the issue I personally have is I'm a medic main who wants to improve. TF2Center is the worst place for me to improve as a medic player because frankly, there is no organisation, there is no strategy and there is no cohesion hence why I described it as aids, probably not the most diplomatic of descriptions but that's what I used to convey a point. Pugchamps also suffer from this occasionally as well but all the players there at least have an idea of what the meta is and (mostly) attempt to conform to this.
I actually have been playing quite often on TF2C lately even though I described it as aids because I don't always care about winning or losing. Sometimes I just want to chill out in a casual TF2 semi-competitive clusterfuck environment and sometimes I want to take things more seriously in which case I play pugchamp. However this really is besides the point and my original post was not about what I want, it's about what we need as a community and as a competitive scene.
Trust me I'm well aware that I'm not good enough to qualify for having an elitist mentality and lately I have been getting picked more on pugchamp but this is about where can someone who is interested in the game go to practice/learn the meta and get enough attention to get into more competitive environments. Trying to improve your gamesense on any class is hard to do when you can't rely on your team to do their jobs and this is the problem with sites like TF2Center. That's not to say TF2C doesn't have a place in the community but its scope doesn't cater to the whole scene and right now there is a gap between those who want to take things more casually on center and those who want an open but more serious place to practice but aren't good enough or well known enough to get picked in Captain systems.
Also to respond to your last points.
a) I'm never (knowingly) rude to beginners but honestly every time I suggest something I get ignored, mocked or brushed off by 90% of players on that site and I can't imagine I'm the only one. There is definitely a mentality on the site that what you want to do and what you ought to do are not always the same thing. Again nothing inherently wrong with that unless you're using the site to improve your gamesense.
b) Cloning pugchamp code has already been done but it's not exactly upstanding behaviour and it further fragments the competitive scene into individual groups which then makes it even more of an obstacle for new players to enter the scene as this takes players who would otherwise notice them away from more public forums. (again this isn't about what I or any other individual wants it's about the community).
c) I do get invited to mixes but this doesn't solve the problem of being known about in the first place and again, it fragments the community.