Regarding the practicality of armor and the example of a Roman legionary, the example isn't entirely accurate. First, you should have taken an even older army; they hung trays on their chests – that was their only protection. Weaponry evolves over time, and if you're looking for an example of reasonable protection, look at the 15th-16th centuries. Even then, these would still be the optimal options for that era, and nothing more. Metals, mining technologies, and manufacturing processes improved. The Romans, however, mainly fought against the wild tribes of contemporary Europe, where there were no states or regular armies. Their enemies were less well-armed and less well-protected, which is why their equipment was the way it was – tailored to the environment.
Second, you see, Reven, it's not wise to consider soldiers as an example. Yes, soldiers will have very good, if not the best, armor... But! At a certain cost. No one will spend money on expensive, good armor for ordinary soldiers. The price/quality ratio is always chosen. Look at the centurion. Here, there's already leg protection. The arms are still exposed, but the left is protected by a shield, and the right needs to be used for fencing; even on later armor, the right arm was always less protected to facilitate maneuvering. And the centurion is also just a soldier, analogous to our sergeants, so again, it's a matter of price/quality. You might as well mention Japan, where they didn't spend money on the army, and peasants bought heavier and larger sticks for themselves, and went into battle naked because they didn't have money for armor, and dirty clothes, if they get into a wound, will only make things worse.
Regarding the main point – Reven is right. Regarding the legionary – Reven, think before you speak.

