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During the Roman Empire.. everyones armies pretty much had the same technology .. swords, bow/arrows, maces, etc ... the playing field was about equal as for wartime technology.. the only thing that was different was the size of armies, the conducting of the war, and how well trained the soldiers were.
That is just so wrong that it cries out for a response. The technologies were not the same. Who else had ballista?

Who else had catapults?

Nobody else had the discipline, weapons and training comparable to the Romans. Most of the peoples the Romans fought still fought wars as single combat, not in formations, such as the testudo(tortoise) formation and other basic formations, as the Romans did.

"...the peoples the Romans fought still fought wars as single combat..."
Adopting the Roman form of formation fighting, seizing hardware and equipment also helped foreign armies defeat them.
Consider Hannibal. He had learned their tactics during the previous years of war against Rome. Though he got beat in the end he did put on a good war.

FWIW, the last "catapult" is in fact an onager -- powered by twisted ropes. I've built one: it's amazing how much power you can get from those ropes. And they squeeze like anything -- my throwing arm is a hickory axe handle, and the ropes actually leave indentations in the wood!