The server I frequent has people who tend to do that. But because I got strange haunted equipment on my sniper I'm more apt to simply clean the sentries out from afar.

There was an instance though this evening when Merasmus called in for a spell. I had the one firestorm spell and I cast it on the area where the other team is teleported to when he casts his own. So by the time his spell hit my own killed off half the enemy team before the whole thing was finished. In the end I had a ten kill streak on my rifle from that and I ducked away before they could steal it away.