Low agreeableness will actually be extremely useful in many use cases, such as scientific discovery and of course programming assistance. It's amazing that this venue hasn't been explored more deeply.
Are we talking about something other than Agreeableness in the personality research sense [0]?
The strongest form of your argument I can think of is “willing to contradict you when it thinks you’re wrong”—but you can disagree agreeably, right? The current-gen LLMs certainly have with me, perhaps because my custom prompt encourages them to skepticism—but they do it so nicely!
No, the concepts are linked, agreeable people don't want to be rude and most people see disagreements as being rude no matter how you frame it. You can't call a woman overweight without being rude for example no matter how you frame it, but maybe you want an AI that tells you that you weigh too much.