I'd rather work with competent strangers who are sufficiently polite than get dragged down by friends who can't carry their weight. No need to mix personal life with work life.
Given a collaborative environment, I'll always choose agreeable/worse. Because with the disagreeable/better collaborator, I suddenly have a barrier between potential productivity and output: I have to co-ordinate with the asshole.
Your personal bias towards agreeableness as a universally good trait is muddying what I think is an otherwise valid point, that people are more productive working with people they like (and sometimes, they like working with disagreeable people, as hard as that may be to believe).
Agreeable/disagreeable is a subjective judgement, and I'm the one making the judgement in this scenario. Whether someone is agreeable and whether I like to work with them are synonyms.
The conversation was generally talking culture fit and not universal qualities, after all.
Honestly, a lot of the people I'd consider disagreeable to work with are actually so overwhelmingly positive that it makes me feel like a cynical asshole if I don't severely self-censor. To the wrong group, I am the asshole.