So far - without any multiplayer experience and only a few skirmish matches - I'd join the faction that says 'It's not a great weakness ... but somewhat irritating'. And I agree with Ryebread: Corvettes do seem to be a little too good. It's slightly silly that they can take so much damage - even from capital ships - yet annihilate fighters and bombers in a heartbeat. At least that's the way it sometimes looks to me - from the imperial side, of course. Fighters certainly have their uses, but it wouldn't hurt the game at all, if they'd take a little less damage from corvettes - and indeed, it could also be a nice idea to let them be of moderate use at attacking corvettes. In my opinion, capital ships can use a bit of help there.
Mmmh ... though this might seem a little one biased towards the Empire (it is, after all - who else is there to save the galaxy?
): I think tie fighters should be better at attacking x-wings. They are the obvious counterpart, and just because we Tie Pilots lack shielding, it doesn't mean that we are worse pilots than the rebels or that our vessels should be considered sub-par. Yes, they are mass-produced ... but crafted by the loving hands of the best imperial construction droids!
Therefore I feel obliged to protest: Tie Fighters are not cannon fodder for X-Wings!
Even for the sake of balance in this simulation, I fail to see a reason for their current weakness - after all, there is not an endless number of ties aboard star destroyers anyway.