these errors are so small, no one will fly at exactly the correct speed for exactly the whole leg, at precisley the correct heading. which i why the dead reckoning method works, and if from 30 secs/1 min away from your waypoint or further if you see it simply fly to it! would be interesting to see how many UAS studes have bust airspace in comparsion to ppl studes..i agree the proper planning is needed but in real life it is over the top.
Glider pilots regularly fly in excess of 500 kms without calculating any of this before they fly, just drawing a route on the map.