The EPA was utterly gutted over the past 4 years. The sad part is that it takes much longer to rebuild than it does to tear down. The EPA being unable or unwilling to enforce environmental protections is by design.
Supposing the EPA is gutted as you suggest (my sibling comment suggests otherwise), it surely still has more capability and expertise when it comes to environmental regulation than the FAA. I think expecting the FAA to act as a surrogate EPA is expecting too much.
The EPA headcount was 14,779 in 2016 and was 14,172 in 2020.
https://www.epa.gov/planandbudget/budget