I say it's easy. How the Executer actually is deafeated is after the sheilds are depleated a tie fighter accidently flies into the bridge, killing all the officers and destroying the navagation. Sure, very few ships from the Kotor era may be able to take down it's shields but if they could then it would be very simple to win. Just be a kamikaze
Also about the convo about wheter nukes are used in star wars, they have been but many of the races believe them to be crude, and underpowered compared to other weapons such as a proton torpedo. (Which was developed in the Kotor era, they are used by the Ravager when it's invading Telos.) I also think during the time of the new republic(After the rebels win against the empire.) they(Nukes, I mean not Proton torpedos.) are outlawed.(I remember reading that in a star wars book a while ago but I am not sure if that is true.)
So, I think the Ravager could defeat the Executer.