@Brian-McG and @Brett-Bartick and @M.-Schrijver, to add to the confusion
I recently learned that since some recent version low resolution tracks are being included to routes. So, my previous claim from about half a year a go is not really valid anymore. Fact is that nowadays, when navigating "track-as-route", you indeed get a track that should look like it was originally planned, instead of being calculated at the time of starting it in navigation.
Personally I indeed saw an increase of sync-time that could be explained by this, but I have no clue as to when that started.