The FDA rushing the approval of vaccine that might turn out to be unsafe harms their credibility in the long run. The worst case scenario of a hastily approved vaccine is so high that it probably makes sense to bear the cost and take the health/economic hit.

Also this is the first major use of mRNA vaccine, scientists and experts were not sure how well it would work. Administering it without trials could have led to a nightmare scenario for a few individuals and anti-vaccine stance for a larger chunk of population.

Ben is probably right, the status quo should change, but I am not sure if the 'opportunity cost' calculus he makes is accurate in this case.