in terms of the EU I always felt the New Republic really failed to fire the imagination with new ship designs period - and what stand-out ideas they did have were often couched in terms of how buggy/problematic they were. I fault it as a blind spot in the authors who focused more on other elements (not saying those other elements aren't important or even more important, but that they drifted away from the WWII adventure serials Lucas drew inspiration from and that were an important bit to the movies).
I've always felt the INCOM design team that defected with the X-Wing apparently never doing anything afterwards was something of a wasted opportunity. Seeing the new stuff coming out of the Rebels fighter skunk works needs to be a thing.