I don't think there's any objective way to say that a majority of papers are bullshit, even if they are. Failure to replicate is "easy" to show, but doesn't say anything about the utility or quality of the science done, beyond the absolute basics of a paper describing what a scientist did in detail and not lying about the results. A "sky is blue" paper will replicate, but I'm not sure how you'd find a "fair" way to call it useless.
Anyway, jumping from "50% of papers will probably fail an absolute bare minimum test" to "90% of papers are garbage" is subjectively reasonable to me.
If 90% seems shocking to someone, I suggest they skim a bunch of papers and develop their own feel for how bad the situation is.