Star Wars ships being faster is dependent on them following pre-charted hyperspace lanes. If something isn’t on a hyperspace lane, they have to travel at sub-light speeds. The Enterprise could warp to the other side of the star system in an instant and then wait hours for a Star Destroyer to catch up. Or go to the neighboring system that isn’t on a hyperspace lane and wait years for them. On the other hand, the ISD could cross the galaxy in a few days, provided there’s a charted path there.