I got lost trying to keep up with him.
Your points are valid , I assume but have no real knowledge to judge.
(Low knowledge/experience level armchair simmer here.)
But, there seems to be a real difference in the ATC Flight Plan, as filed, and the airplanes Flight Plan and the airplanes flight.
ATC seems to have no knowledge of where you are going and
your heading, with AP or not.
It tracks your reaching its waypoints in its Flight Plan and
has no idea of how you get to its waypoints.
Thus, it cannot give you a vector from your location to the next waypoint.
ATC doesn’t know where you are.
ATC can only give you a vector from its last waypoint that you reached to its next waypoint.
If you are not flying the Flight Plan you filed, then you are in trouble.
ATC cannot help you.
You have to get yourself back on the Flight Plan.