I agree that having someone a higher rank in the multiplayer lobby seem to cause anxious to another player - especially entering a room with most if not all players are in high rank - in addition I also believe that beatmap choice and promoting are another factor here.
Beatmap choice - Whether it'll be the length of the song, mapping style, star rating on which people are comfortable to play with; these could vary people's interest to play the game. To give a few examples: Some players prefer short length beatmap so that they can play a few rounds quick in a short time, and some will not participate with complex mapping like aim control map, since they aren't quite ready to deal with that - or just have a general dislike on it. :b
Promoting - For promoting-wise, it is unlikely that you can promote anywhere in the channel except #lobby - supposedly, but the harsh truth is that not many people are also interested to be in #lobby. Other than that, I can suggest having a multiplayer room to be player-friendly - making the title unique and interesting - and that is targeted to most players such as what the other auto host rotate rooms did to gain attractions.