Yeah, I agree (and the spoiler really doesn't change things). Having your test subjects get sick, miserable, and eventually die would make sense for controlling them. Having them be cheerfully, gleefully evil and destructive makes absolutely no sense unless the destructiveness is actually your intent!

Despite having watched the series before, this had never occurred to me until alessandriana pointed it out; I'd just assumed that the violence was incidental and the real point was to make Arnaud's subject dependent on the drug (and him). But it fits a lot better if destruction is the actual goal!