> Could you or I be 100% certain we wouldn't react the same way?

Probably not - but when I say that we should not deemphasise their agency, I don't think I imply otherwise. The opposite, in fact: to even ask or try to answer the question you ask here - to consider how I would act if put in the circumstances of another person - is to view their suicide as agentic.

(Observe that you could not meaningfully ask, of someone who got lung cancer and died due to asbestos exposure, whether I could be certain I would not "react the same way" to asbestos exposure! That is the difference between the "disease" framing and the "act by an agent" framing.)