No it's not. Your asking me to compare an Imperialist Democracy and a band of Luddite Slaves over the course of 1000 years; okay, where do you think that the Legion will be in 3281?
You sound like you don't understand the question.
IF the NCR survived for 1000 years, they would be more likely to have discovered how to use Nucelar weapons and therefore blow themselves up, again.
The Legion on the other hand, if they managed to survive for 1000 years, they wouldn't blow us all up.