My interpretation of the Final Order was that this was something Palpatine wasn’t able to start developing until he had the resources of the Empire at his disposal (at least that was what I took the Star Destroyer design to imply). I don’t know what the visual dictionary says so I can’t comment on that. Really the main thing that bothers me is it just feels redundant. Wasn’t the First Order the same idea - a mysterious resurrected Imperial force that had been building power in the unknown regions as part of Palpatine’s contingency?

They didn’t seem to have a solid grasp on the interplay of the two forces, and they could have done something interesting with some friction between them if perhaps Palpatine claimed some ownership of the First Order’s existing fleet and they weren’t necessarily on board. They could have at least made it seem like they were part of the same plan. The First Order comes in to destabilize the galaxy, the Final Order finishes the job (but Kylo becoming Supreme Leader complicated matters).