I've had troubles with this mission myself, not troubles winning since I can take down the shivans myself, but as some of the users have said...
I've seen the corvette doing nothing at all while I was beated to death, and my wingman were useless, they died in the first 2 seconds even giving them orders to attack before the shivans arrived.
The second wave of maras (after the first meson fails to destroy the knosos) does nothing at all, they just fly around happily while I shoot them down.
I don't recall this kind of problems, but It can be because of something I did different too.