Another thing to consider is that, as far as we know, Frontier hadnt been in a battle at all, or at least in many years. Their pilots would be raw whent he series started. Now we've seen a few battles, they'd have been training harder, better gear etc etc. I dont find it surprising they won.
Also Macross didnt exactly kick ass in the series at first. As i recall it, the Zentradi were studying it and sending probing attacks, not full on trying to take it out. If they had wanted Macross destroyed earlier, they could have done so before the huge fleet at the end showed up.