It's not a fiction. People do their jobs even if they don't like the current or past President. I'm sure you can pull out a long list of people who didn't, but unless you name everybody, it simply isn't a fiction. My claim isn't bureaucrats are always apolitical, it's that they mostly are. Showing that some aren't doesn't show that they mostly are.

Take the executive assistant to the American diplomat to, say, Sweden. They file paperwork and schedule appointments for the diplomat. Their role is operational. Logistics stuff. Coordinating what goes where. Setup a meeting between three very important busy people and juggle their calendars. Does that position really need to be someone we vote for? They do operations, not make policy.