There are plenty of debates over what was the greatest, strongest, longest, or most influential empire in world history. Much of this debate is based on opinions and terms that are rather broad, especially in historical or political ways. But Rome has left such a permanent mark on history that it’s impossible to see post-classical history without their impact. The largest religion Christianity, the Orthodox/Catholic split, the Crusades, the largest war (the Fascists of WWII introduced neo-classical culture and reintroduced Roman militarism to fuel the war), the concept of Europe, the rise of the concept of Republics, modern military policies and tactics, and don’t forget indoor plumbing: it’s gonna be big. I personally cannot say if Rome is the greatest empire ever, but I would easily put it in the top 3 primarily due to the magnitude of its influence that still is strong today. And to build and maintain such an empire, a warrior would be needed to take on any army of its time: the Legionnaire.
Now before I address anything else; I need to mention Lorica Hamata and Lorica Segmentata: or Roman chainmail and Roman plate armor. The Segmentata literally means segmented, I do not know how this would affect its ability to withstand stabs or blunt force, and it doesn’t cover the limbs: but it should in theory be on par with iron or steel chestplates. The segmentation does make repairs easier since you only need to replace the individual segments instead of the entire suit: however this does also mean that focusing on a single region or segment of the armor can make the segments fall off and thus make the warrior vulnerable. So while easier to repair, it isn’t designed for longterm endurance during the battle itself.
According to my references, for the majority of the Roman Empire, Roman volunteers had to buy ALL of their weapons, gear and armor to enlist in the army. This actually led to recessions and riots as some soldiers went bankrupt to pay off their war debt instead of having that be the responsibility of the Empire.
Not to mention that the Hamata looks very Medieval and bland while the Segmentata is so unique and iconic that Hollywood would probably prefer to depict the latter. So while both armors did exist and some Legionaries did afford to buy the armor: the Hamata would be reasonably more common.
A Muscle Cuirass, similar to Greek chestplates, would clearly be more expensive and for generals primarily.
Either way; the Legionnaire lacks face protection (although their helmet is effective against side or indirect blows) and they lack protection of their limbs. I don’t see this as too much of an issue considering the Scutum is one of the best shield designs I have ever seen; their curved edges and blunt round center is specifically designed to deflect blows away from its center and thus protect the Roman. I will point out that Shield Bashing isn’t going to be as lethal as a spiked Targe or the sharp edges of a Spartan Aspis: but it is able to ram into the enemy to allow the Roman to get in close and go stabby-stabby.
The Gladius has great steel, but it seems to be just a basic short sword. How would such a blade rival the fame of the Katana or Broadsword? Simply put, because of that Scutum: the protection of the shield allows the Roman to be aggressive and reckless while avoiding harm. Closing the distance with a charge and attacking at your effective range is tactically effective: any warrior wants to obtain and maintain the range they are most effective at. The Gladius being short works because a heavy long-dagger assists the aggressive mentality: a good attack combined with a great defense. And while designed for stabbing, it is also thick enough to slash very effectively.
It is absurd how little information exists in regards to the Macedonian Wars: but from what I researched; the Hoplite, despite being one of the best tanks thanks to their large shields and long spears, were countered by the Legionnaires. The Pilum was specifically designed to dig into an enemy shield, get stuck and break on impact. This makes the shield have extra weight, which made it too heavy to use. Without the Hoplite shield, the Scutum can just block and bash the Hoplite spears out of the way. The fragility of the Pilum is actually a benefit, as the enemy cannot use the Pilum against the Romans. Celts, who had similar spears and shields but less armor and discipline, were even more vulnerable to these Pilum tactics.
Legionnaires are such great warriors that what led to their downfall was actually not conquest, but financial ruin and ‘barbarian’ influence. The last centuries of the Roman Empire had the common Roman soldier look more Celtic: using a wooden round shield and a longspear.
The Legionnaires are relatively slow and predictable. They are better designed to be in an army instead of 1 on 1 combat: protected by the Scutum of their adjacent Roman (as even a shield as massive as a Scutum isn’t perfect). A Legionnaire is designed for close combat: that’s why the Gladius, not a Bow, is his most famous weapon.
The Pilum is great against heavy enemy shields, but it’s normally thrown into volleys to guarantee hits. Javelins are not the most precise weapon, and their range is also very limited. Scorpions and Ballistas were also primarily used for sieges or against armies: lacking the rate-of-fire or precision to be effective against individuals despite their massive range. An agile combatant would avoid the Legionnaire’s projectiles. However I wouldn’t recommend a ‘Fragile Speedster’ character like a Ninja since the Legionnaire would have a defensive advantage, and spears are also not recommended as Legionnaires were trained to parry and deflect spears to defeat Celtic spearmen.
To defeat a Legionnaire, you would need to be agile enough to avoid the Pilum, but have the range to avoid the signature Gladius, without relying on a spear, and be able to last long enough to get around the Scutum. I’m thinking an armored yet agile swordsman, designed to be flexible and an effective 1-on-1 fighter. It’s no surprise then that the Rajput was victorious in his episode against the Centurion.