Romans as no-retreaters

It is not quite true that the Romans never retreated. They tended to
have a very strict system of military discipline, and a bad performance
could get your cohort or legion decimated (one man in ten executed) so
if the order was to not retreat, they probably would not. But it did
happen once in a while.

And I don't think you can point out that their engineers had a similar
attitude - the desire to overcome huge obstacles to assert your
fundamental rulership of the universe where doing so will not kill you
dead can't exactly be compared to standing and fighting when that could
often get you dead.

This had more to do with their psychology and the way they organized
their society and their military than any necessity of the race. They
were just as varied, just as adaptable, and just as flawed as most other
iterations of the race (maybe a bit more successful than most).