The difference between the endings of ROTJ and TROS is that the former was concerned with a small ‘insignificant’ rebellion targeting the head of a galaxy-wide Empire which has had 25 years to become entrenched, whereas the latter merely prevented a new incursionary force from gaining a hold on a galaxy that had been under the control of a democratic republic for decades.

As much as I give TFA grief for resetting the universe, there’s at least a good argument to be made that the Empire was too large and established to be defeated as easily as it is portrayed in ROTJ, thus making some sense of its return. There’s much less reason for the First Order to come back, since it was never well-established and was defeated by a popular uprising from all corners of the galaxy, not just a small military organization like the Rebel Alliance.

I don’t like the way TROS handled things, but at least now there’s a good case to be made that things are different now, as opposed to after ROTJ.