Great question, and I look forward to following this discussion!
A tangential (but important in my opinion) comment… You write that “EA funders have funded various organisations working on biosecurity and pandemic preparedness”, but I haven’t seen any evidence that EA funders aside from Open Phil have funded biosecurity in any meaningful way. While Open Phil has funded all the organizations you listed, none of them have been funded by the LTFF, Survival and Flourishing Fund, the Centre on Long-Term Risk Fund, or BERI, and nobody in the EA Survey reported giving to any of the organizations.
The LTFF has admittedly made some small biosecurity grants (though as a reference it has granted ~19x more to AI), and FHI (which has relatively broad support from EA and/or longtermist funders) does some biosecurity work. But broadly speaking, I think it’s a (widely held) misconception that EA donors besides Open Phil were materially prioritizing biosecurity grantmaking prior to the pandemic.