Yeah obviously it would be much better if the First Order having its roots in the Republic was stated in the opening crawl for TFA or something.

Independently of expanded canon, I always got the idea the First Order had a mixed origin: partly from an Imperial remnant (explaining its military junta style, brainwashing of child soldiers, Snoke, etc.) and partly from a secessionist New Republic party (giving the First Order legitimacy and providing most of their resources to rebuild their fleet). I really hope the Mandalorian provides us with more hints to the origins of the First Order. Apparently not everyone was pleased with the restoration of the Republic and it would be interesting how this point of view would have helped the rise of the First Order.

And yeah it would have been great if at least some hint to the political future of the galaxy was given in the epilogue of ROS. Ideally, they would have left some kind of message, going from “kill the past” to “learn from the past” both for the Jedi Order (have Rey acknowledge the old Jedi were flawed, and setting off to build a new one) and the eventual successor of the Republic.