This would work great if every state and city government was competent and good at disaster relief. In general they're not, and FEMA already rely too much on having competent local government that they can co-operate with - in particular, I get the distinct impression that a lot of the disaster relief problems in Puerto Rico which were blamed on FEMA and the federal government were actually the result of the local government being completely and utterly useless (infamously so, even).