Well I think the core issue is, that here 1 server as one physical entity is configured to only offer 1 map at any time as logical entity, as one-trick pony.
I mean it should be possible for server admins to just offer the phyical service, and having players an easy way to decide for content... and yes, map voting really just doesn't cut it...
BTW: If multiple people join the server, there will always be 1 that is the first to arrive at the server-core-loop. And starting to download a map is designating the server for this map. There just cannot be two absolutely simultaniously entering for different maps. If the unlikely event ocours that two player in a very small timeframe join the same server for different maps, the second will just find himself in a map he didn't join, because of the other being first to designate the server. No big problem IMHO.
I don't know if offering statistics if help server admins. Look in the reality of the serverlist, for a caring server admin a little common sense should already tell you, that the map you offer is hardly ever wanted while others are almost always close to full... it just doesn't seem to really work...