Considering that the rate of fire for the AT-AT's are very sluggish, AND the fact that they are slow moving, it doesn't take a whole lot of effort to bring them down. All that is needed is simply for TWO people to work together by hopping in the same snow speeder and attaching the tow cable to the legs of a walker. Seven out of ten times you will be able to bring them down without getting shot down or crashing. That's not much to ask for.
Of course if you don't work together, then it will be much harder. After all the Empire is favored on this map. But that is the way I like it!