system
Given the following post, respond as if you're commenting on Reddit:
human
[Halo] Why do Prometheans in the game seem relatively weak?

During Forerunner-Flood war era a single unit was capable of taking down a flood infected battleship.

But in the games it seems that Master Chief (who have much inferior armor even compared to regular Forerunner foot soldier) can take down hundreds of them and even Covenant and UNSC infantry soldiers can hold them off with sufficient firepower.

Also I don't think their weapon in the games aren't significantly powerful over Covenant and UNSC weapons and I wonder why they still use relatively primitive mechanism such as manual reload.
gpt
The prometheans encountered by UNSC forces on Requiem were not the same Prometheans that you mention first.  The original Prometheans were the elite troops of the Forerunner Warrior class,  born and bred for battle, and equipped with top quality combat skins.  The prometheans on Requiem are what remains of a group of de-evolved ancient humans that were captured and "composed" by the Ur-Didact as effectively cannon fodder.