Theories abound inside. And so many spoilers.
This clarified a few things I was annoyed about seeing the movie. In particular When Leia had a ragtag band of miscreants and NO YWINGS FOR A BOMBING RUN. USING NO BOMBERS. And why the Republic wasn't actually "The Resistance". And a good bit about the sociopolitical climate of the fledgeling Repiblic... as it gets crushed about 1.5 hours into the movie as they blew up the entire New Galactic Senate offscreen without 10 seconds of commentary as to what had just happened. This movie really had wayyy too much edited down. But I'm hoping to see a much better Extended Edition someday soon. Good post!
In universe, they totally could have used Y-Wings in that movie and it would have made sense. Those things are like the Ford F-150s of the star fighter world. They've been around forever (since the Clone Wars) and everyone and their mother knows someone that has some. All you have to do is get onto Jedi Craigslist, type in "Y-Wing" and bam! Page after page of cheap, easily obtainable star fighters.
That said, some questions on there don't really need answering, such as the clone army. Other questions though, such as who the Resistance are and their affiliation with the New Republic could have easily been clarified in the movie within a few minutes and a few sentences. I kind of chalk that up to sloppy writing.
Shouting out to you PlaceboEffect so you're not left out of this loop.
I wanna see more knowledge ywing bombs in VIII... I agree. They cared alot about it making sense. Perhaps more than the new writers did....