Just thought of this, Force Auto Team Balance (Targeted for TD, but can be effective in any team based game).
This is so clear, just have the 2 teams be auto balanced to be as fair as possible, instead of being forced to wait in a lobby until the team balance is gone, Its very, very annoying especially when I have a party of 4 or 5 join in, and being the Rank User Magnets we are (Usually goes me Obby, 1 Emerald, and 3 Diamonds) everyone flocks to the team we are on for being "really good/very skilled" just because we are ranked, so much so that we started taking into saying this "Ranked Users are not better than normal users, just because we have a rank doesn't mean we are good" (sounds very hypocritical because if you have ever played with or against us, (as in the party of 4 or 5), we play very well)
but I can hear you saying what if there is a party, as what YOU said.
Simple, either bite the bullet and accept that your party can be separated, or keep the party together, or if possible set a command or something like that to allow party separation or not.