When you're gonna compare two things and say one is indisputable and the other is weak, cite some claims.
PFAS are real, test your water from your tap today. Any carcinogen is detrimental to health but depends on exposure, same goes for PFAS.
Smoking causes cancer? Stop smoking, and prevent people from smoking near bystanders. Asbestos causes cancer? Ban it in new products, and mandate secure removal for existing stuff. It's not that hard to deal with: just stop using the harmful thing and it'll be fine.
PFAS causes cancer? Permanently condemn all contaminated land, kill all wildlife trying to get out, mandatory cremation for all humans who lived there, and a total ban on breastfeeding for mothers who lived there.
PFAS might not yet be definitively proven to be harmful in limited quantities, but the bio-accumulation is bad enough that we just cannot take that risk.
I think you can emphasize your point by noting two categories, those which bioaccumulate and those which don't, but the exposure of things bioaccumulated is, to your point, endlessly extended.
Lots of things bioaccumulate, but cause no problems at all.