that's the trailer game-plays not going to be the same... As for lights raining down bullets on the heavy's that would only work if the heavy's didn't look up... Cause if the heavy's look up and start shooting the lights would have to move back or die.... So heavy's would just keep walking and go throw the map without a problem...
I don't think they are immune to everything. I'm pretty sure that guns and explosives can hurt them too. And they could just flank them. They wouldn't stand a chance head on, but if they used their environment, and gain vantage points unreachable from heavies, than they could have an advantage. If it comes down to skill, and each team plays each of their roles perfectly, it is anyone's game.
Also, there is an objective in the container city where you pick up the robot and drop it over the resistance, although it doesn't kill anyone because nobody is standing there. So who know maybe you can.