Usually whenever someone ends up joining late into a match already in progress, it's because one team is getting completely slaughtered and no one has the capability to do anything useful, and the poor sod joining is immediately thrown to the wolves. I've been put into a team losing by over 900 points about 5 times in a single day. To fix this, just completely remove the possibility of joining late unless it's a friend's match. And to show people what their friends are doing, they can take a page out of Destiny's book and give info on the battle their friend in question is in, including score and map location.