Caesar talks a big game about how the Legion will change and absorb the best of the NCR when it takes them over. This isn't historically too impossible as Militaristic Sparta changed a lot from taking over Democratic Athens. Caesar talks about it like it's an inevitability and he doesn't seem to mind at all if it happens- he almost seems to look forward to it. He praises NCR as being culturally superior to every petty tribe he's dealt with. So what do you think would happen in the Legion did march from the Boneyard to Shady Sands to Arroyo and take over everything there was? From a moral viewpoint the Legion would have absolutely nowhere to go but up from a synthesis and from a competence/non-corrupt point of view the NCR would have nowhere to go but up as well. It actually could be a pretty good marriage between the two.