Lethality is... weird. Cyberpsychos in particular seem to always take non-lethal damage, I guess as an anti-frustration game feature.

I used a katana for most of them and as long as I didn't accidentally give them an extra hit after they started falling down, it was fine. Conversely, I had a "non-lethal" automatic rifle which almost always killed them since at least one extra bullet would hit them after they went into their falling down animation. You can still accidentally easily kill them even with Gorilla arms if you're spamming attacks.