You have to consider the time that the State of Rome existed for. The senate ruled from 509-31 BC... The Emperor up to 476 in the West and 1453 in the East So you are talking over 2000 years. Yes the Romans didn't make the best armor early on and they did learn a lot from conquering the Celts but the point I make is that the quality of metal wasn't the be-all and end-all. What made Rome so successfuly was their training, organisation, leadership, innovation and a multitude of other factors that less centralised tribal societies couldn't compete with. Weapons alone aren't enough. For instance the ARVN of South Vietnam had superior technology at their disposal but still lost to their Communist enemy Also iirc Roman soldiers had to pay for their own gear. So if you could afford a higher quality steel blade you could buy one. But realistically in a battle you might kill 3-4 people so there is no risk of a blade going blunt.