I've made it in the original ST, but there it was only ONE leviathan
Anyway it seems like the leviathans aren't the main problem. I considered what QuantumDelta said about the hercs- a wing of hercs are jumping in (about one click away from the pods) a few seconds after the cruisers. And they're not distractible, they just keep firing on the pods until everyone of them is gone. I haven't noticed that until now because i was fully concentrated on the cruisers... no wonder, two leviathans in front of a few escape pods are a real attention getter.
Well i managed to kill 2-3 hercs, but at least one of them survives long enough to blow up a pod.
Maybe some other guy will get that bonus goal some day, i give it up.
Something surprises me- the mission is quite easy to complete once you use the right tactic. The pods are set invulnerable until the Soyakaze arrives, so there is no need to protect them until the science cruiser is down. The wingmen's preset orders are to protect the pods/destroy the science cruiser, and they'll die very fast whilst they try to accomplish these orders, and the time pressure after the science cruiser is down isn't helping.
But if you order them to ignore the science cruiser/attack all enemies, the GTI fighters will drop like flies, and the own wingmen won't be scratched very much. After they're down, just order all fighters to the first thee escape pods to protect them and wait until they're in position, destroy the science cruiser solo, afterburn to the pods and wait for the cruisers and hercs. Two leviathans don't survive very long against five intact wings, especially because they're entering the combat zone so very close.
Only the hercs remain a problem, i just couldn't stop them fast enough.