What is your source for this? USAID has an inspector general like every other government agency. Inspector generals are independent of the agency and part of their function is to perform audits. Congress has the same powers with regard to USAID as it has with any other agency. It can investigate, subpoena, etc. The senate must confirm nominees to lead the agency. USAID is subject to the same laws like FOIA as any other agency.
What does it even mean to say that the state department is by definition political? There are political appointees, but the overwhelming majority of the state department is career foreign service or career civil service, which are apolitical. The same is true for USAID.
None of what you're saying makes any sense or has any relation to reality.