That's the reason it's active players "job" to try to organize their xonotic playing into a schedule, like alot of people do atm.
For example when I get home from work at around 20:30 I know I can find a full minsta server to play on if I want.
Similarly I can find a full deathmatch server during 9:00 - 12:00 during the day.
If you guys have some sort of schedule that doesn't change much, playing during the same time or close to the same time of the day could help improve the playerbase, because new players begin to know that they can log on during, say... 20:00 and find a few servers to play on.
Eventually this can expand out of the minsta/overkill servers that are very popular and jump to duel/dm/ctf (vanilla) and even defrag/race.
Besides that, if you invite a new player, ask him to play during the time a server such as dcc, mon or esk is active, asking them to duel can put them off and make them quit, while it's alot more likely that they stick around if they can jump in for a few frags without the pressure of a 1v1 game.
About skill, that's a tricky one. You have to consider that some players don't play competitively and the reason they don't seem to get good is beceuase they don't really put any effort into improving. It's true however that some players pick up skills slower than others, and this can be due to many factors.
Here is an example:
Myself; I started playing fps games, starting with starsiege tribes and ut 99 when I was 6 years old, that's 10 years ago for me. Eventually when I got into ut2004 I started playing competitively for some years, around 16000 matches, both minsta and weapons. When I got into xonotic about 2 years ago, I tried getting into the competitive scene here, and expected to be really good after playing so much time... Well.. I was wrong, I was, and still am pretty terrible, but that doesn't mean I'll quit, I just took some time to rethink my playstyle and got right back into it
Similarly I know a lot of players that just run around playing casually in dm/ctf servers and never really "improve", but when they get dragged into the competitive scene they can get really good fast.
Now my point with this, is the focus on "new players" should be to get long time fps players into xonotic. Now, while completely new players sounds attractive, it's hardly realistic, since unless the gaming industry takes a 180 turn, they will prefer to play something like planetside or battlefield in which they can quickly and easily get into the game.
Such as checkers (simpler but not easy) boardgame is attractive to most because it's easy to learn. Chess on the other hand, has too much depth and has a steep learning curve that most people are not willing to put time into.