After working inside the government for over 20-yrs, and as an international businessman for the past 10-yrs, I can say that perhaps the Ambassador or the DCM may be like you, but it is the FSO’s that do not act in the interest of the US. I have seen it firsthand. At best, the FSOs act like they are the “honest broker†between the US and the host nation. At worse, they actively work for the host nation and derail US policies they deem unworthy of support.
The dirty little secret is that the State Department is just the storefront operation when it comes to foreign policy. The NSC, DOD, and the intelligence agencies have more sway than the State Department when it comes to formulating policy. Two thirds of the American staff at our diplomatic missions abroad are from other agencies.