As far as I'm aware its usually just one server being filled at a time. I will prefer to sit and wait for an empty spot on a full server than start populating a new one. Question is, are there enough people doing the exact same that we could decently fill up a server? It would be nice if this was more visible, including how many unique players logged on but never entered a game so players can know what to expect. "7 players in the waiting room, 4 players left without joining a game in the last 30 minutes" gives you a good idea of how many players you could expect of they all joined an empty server.
Or maybe there are better ways of handling this? For example you can join a server, but use a button to check current server status so you can leave and join a full one if a spot opens up? That way players are filling an empty server waiting for a spot and eventually might be too invested as more players join their "waiting" room.