I think that the most powerful reason that the Prometheans are a lost cause is that there is nothing to relate to. What does a technologically illiterate proto-human trapped in a robot body for 100,000 years think when compelled to kill humans?

Do they recognize us as kin? Do they remember their proto-humanity? What is it like to be a 'deevolved' human?

And then how is this expressed during combat?

Would it be like head-crab zombies bemoaning their fate?

Would it be like fighting legions of Marvin the Paranoid Android? (only infinitely less intelligent)

Would this make fighting them fun?