We wanted to lure raptors into the Imperial camp first. Vasilik apparently had a plan for doing just that. While the raptors are wreaking havoc, Scarlet sneaks to an AT-ST and starts blowing the crap out of everything, with the other AT-STs as first priority.
I believe that was the gist of it. We're there for when things go horribly wrong and we have to kill Stormies.
If we don't steal a walker and lay waste to the others, we
1. Are more likely to be killed, as the Imps will get in the walkers to kill us.
2. Won't be doing much to help our cause, because a pack of raptors and a rag-tag band of Rebs can't put a dent in the Stormie numbers. We have to break their firepower, not their manpower.