Chief Hanlon’s mistake was in assuming that the legion will stop with Hoover Dam; people like Caesar don’t stop taking until either someone else stops them, or there’s nothing left to take. If the the dam is lost to the legion; Caesar isn’t going to be satisfied; he’s gonna think “I am completely invincible!” Conquer the rest of the Mojave, and invade the NCR.
Best possible result of that invasion: Ceasar is killed while destroying Junktown, and the legion collapses.
And the worst: the Legion conquers all of New California, and the disaster Hanlon sought to prevent is replaced by an even bigger one.
Anyways does it make sense given ceasars legion is like that? Fuck no! Is Ulysses Fallout “i picked this new name because its meaningful to me” New Vegas absolutely trans? Hell yeah! Absolutely! The fact that in canon this makes no sense is dead and i am dancing on its ashes!