If any of the NCR’s technological and military superiority mattered they wouldn’t be worried about the Legion seizing Hoover Dam, they wouldn’t be asking every favor possible of a single mail carrier and they wouldn’t ever have to rely upon heavily guarded brahmin caravans to supply their frontier.

NCR isn’t operating on a model of development. They’ve already hit the imperialist stage of contradiction where profit is the primary incentive. The NCR’s problem isn’t using their superior military and laser guns to kill a bunch of desert fascists speaking bullshit Latin. Their problem is creeping stagnation and lack of infrastructure.

Legion has been developing territories they conquer, based on stuff Lanius and that one Arizona trader says. You can talk Lanius out of pushing westward because the Mojave isn’t fully self-sufficient yet, for example.

So, based on all that, I see NCR crumbling due to its internal contradictions. Legion moves in west. Traders prefer Legion due to safety of the roads and low taxation. Barons open trade with the east, then it doesn’t matter if it’s Caesar himself or not.