Though, to be clear, I think this is only a moderate reason (among many other factors) in favour of donating to global health vs. say biosecurity.
Overall, my guess is that if someone is interested in donating to biosecurity but worried about the smaller existing workforce, then it would be better to:
Fund movement building efforts to build the workforce
Invest the money and donate later when the workforce is bigger
Though, to be clear, I think this is only a moderate reason (among many other factors) in favour of donating to global health vs. say biosecurity.
Overall, my guess is that if someone is interested in donating to biosecurity but worried about the smaller existing workforce, then it would be better to:
Fund movement building efforts to build the workforce
Invest the money and donate later when the workforce is bigger