Double wall of text incoming regarding ship damage. Y-wing example 1st, then gozanti
It is the power and responsibility of the GM to not let the game devolve into this line of thinking, but for the sake of conversation let’s give this a shot.
---The Y-wings---
I don’t have star destroyer stats offhand, but I’ll try to do my best. I’m going to assume it can angle/boost its shields to get 4 defense in each arc the fighters are attacking in making the difficulty PBBBB to hit. You can assume the fighters run 2 ways (see below), in the spirit of the game, I would place the 25 Y wings into 5 minion groups of 5, making the attack dice pool YYGG (you said they’re double moving to get in range (I’ll forgive that they’re not speed 5), so they would not have the maneuver to aim).
This dice pool results in a 63% chance for each minion group to land a hit, so just over 3 hits for the entire 25 Y-wing attack force. Now, the game2.ca dice roller doesn’t really give the details needed to answer the question, “how many hits will have 2 advantage for linked?” But it does tell me that 15% of YYGGPBBBB rolls will result in having 2 advantage (regardless of if they hit or miss), so it’s unlikely linked will activate anyway. So 9-11 damage (breach 6) per hit vs probably armor 10 means about 15-20 damage per volley will get through to the star destroyer. (Triumphs/advantage could come up to trigger linked and increase this to maybe 4 hits, but it’s unlikely and only adds another 5ish damage)
Now, we know the gamey types would run the Y-wings as individuals (wouldn’t let this happen if I was GM, but that’s not the point) in order to maximize rolls, and more rolls means more hits. So a YYPBBBB dice pool results in a 24% chance for each fighter to hit, so we could expect 6 hits from the 25 y-wings. With only a 4% chance of any given roll (success or failure) coming up with 2 extra advantage (and zero chance of triumph) for linked, I feel comfortable saying the chance of linked is insignificantly small. So 9 damage (breach 6) on 6 hits vs probably armor 10 will end up with 30 damage on the star destroyer per volley.
In neither of these cases will the Y-wings have a hope of taking down the star destroyer in 1 round. I am unfamiliar with the star destroyer’s HT threshold, but it would take no less than 5 rounds to take down a nebulon-B (ht 71 IIRC). Further, the star destroyer would be aware of the Y-wings before they got in range and would likely be blanket barraging to upgrade the attacks’ difficulties. I won’t crunch out a new set of probabilities, but it would be complicating things for the fighters further.