Sats have wild accuracy shifts and depend heavily on the plane being fully operational. Ultimately what you end up with sats anyway is list of waypoints, not anything dynamic, and it can be done with radar as well.
No, they do realize exactly that, which is why quite often the paths didn't change as much as they could and why aviation community tends to rebuke ideas like "remove SSR and PSR because GPS and Mode S + ADS-B is enough".
Sats provide good "happy path" when everything is ok and allow greater density. But approach and departure routes are going to be designed for safety as well, including when those features fail.
GPS and the like provide an efficient "happy path" and a horrible failure mode, which is why there's strong opposition to the removal of radars "because ADS-B/Mode S is good enough"
