Standard fighting equipment for a post-Marian legionnaire was the gladius, pilum, pugio, scutum, galea, and some sort of body armor, either the lorica squamata, lorica hamata, or, mainly imperial, lorica segmentata. This profile rarely if ever changed in any meaningful way, whether fighting naked Britons or Parthian horse-archers or perfumed Egyptians or other Romans legions. This changes in Late Antiquity, when we start to see specialized units, but in your period specialized forces would always be auxiliaries.

Your focus on [weapon type] effective against [protection type] is mostly a modern construction. The vast majority of casualties in an ancient battle happened after a side broke and fled. Ancient battles were much more about maneuvering, positioning, and maintaining morale rather than inflicting damage to combatants along the line of battle. Casualties were incidental to those three, and killing blows often the consequence of an injury unrelated to body armor (like taking a tragula through an exposed thigh at twenty meters, or going down with a sprained ankle in the push).

You should also not discount the gladius. It was a vicious, versatile weapon, and the legionnaire treated it like a tool. Gladius, shovel, wooden stake. Its tapered point made it a sturdy puncturing weapon as much as a slasher, and with the force of a thrust, it was more than enough to push through the weakpoint of a lorica hamata or the joint of a lorica segmentata. The hilt design was intended to help transfer force to a thrust attack in this way.