If you are on a full team it is 1v4 unless your team invaded. It's usually pretty easy to kill the invader before they even get going unless they spawn behind the damage circle. That's were planning and communication comes into play. Send the sentry one way and your invader the other, now on of you are behind the invader, if he goes down the middle you have a reaper and collector waiting and the other 2 are both behind him. People panic and scatter, I see it all the time when I invade but the coordinated team usually takes me out very quickly.