On ISDs vs Fighters as the Imperial Doctrine.
Maybe a wing of fighters could take down a Star Destroyer, if it wasn't protected by its fighter complement, but that doesn't really mean you won. You cannot take over a space station with fighters. You cannot liberate a planet with fighters. You cannot save civilians with fighters. You cannot pose a threat to a city with fighters. Fighters do one thing. The hint is in the name.
Maybe you can do a hyperspace hit and run, to destroy a lone star destroyer on patrol, but what is the point of that? There are tens of thousands of them. The Empire isn't going to miss one of them. But every fighter lost is very costly to the rebellion.
This is why rebels do hit and run missions, this is why they are reluctant to go into actual battles... because they know they can't win. This is why they can't really go and liberate planets. They might be able to take out a few factories, space stations, free a few prisoners etc, but they have no chance in a proper war.
The rebels can only win because the plot demands it. Because imperials have to start killing each other, and be ignorant about their past mistakes, and some key figures have to turn traitor, etc. There is no way they could have achieved a military victory against the empire.