I’ve not once heard anyone use expanded universe work to explain the ST. I heard it all the time when people would defend the PT, but never for the ST.
A common complaint for the ST is that it doesn’t make sense that the FO has all these resources and that it doesn’t make sense that the Republic and the Resistance are separate, while the Resistance is still being funded by the Republic. I really don’t feel like going in-depth with the ST story details because I really don’t like talking about them, but there are common complaints that are addressed in other material.