The trouble with not being a direct hire is that you are treated like you rank one level below the night duty driver.
I’ve only had that experience when in DC. Usually dealing with the career Civil servants who are homesteading their DC area positions. In the Foreign Service, generally, there is a great deal of cooperation and understanding.
With that said, there are those who are driven to achieve, and those who are trying to learn about the culture, and a few who are just along for the ride.
Post to post, there are differences. The “major” posts, such as the great European capitals, Tokyo, Beijing, Baghdad, will always have a heavier “political” presence, due to the more highly visible politics of the post. Career senior level diplomats (ambassadors) in those posts are not exactly rare, but many are those who contributed most to the last campaign, and they often bring their favorite sycophants with them.
Stick with the mid level people and go to the Marine House.
That definitely works best in Europe: I had many a wild night on the road at the Marine House in many countries. In Africa, we hung out with nearly everybody, including the ambassador. It’s a different climate and culture at hardship embassies, where people feel like they’re accomplishing something as a team.