If they killed a bunch of your workers, they have an economic lead. If they have an eco lead, they will get better as time goes on. So what you have to do is find a way to do some kind of damage quickly. Ideally you take a good fight or do some counter harass damage.
Of course, this is after establishing they have an eco lead in the first place.
Probably not. Tanks or liberators would be better most times.