That gpx file does not contain any wpt points.
It contains a route with 23 points and a track.
(GPX tracks do not have waypoints)
Importing the “Route” in routing (50 waypoints), it uses all 23 as waypoints for the route calculation.
Importing the “Track” in routing (50 waypoints), it uses only 50 as waypoints for the route calculation.
So it seems to work as in the description:
“If your route contains less waypoints than specified nothing will be removed.”