It’s such a weird idea that the actor they chose as the face of Anakin Skywalker is ‘wrong’ because of movies made afterwards. Sebastian Shaw works for the Anakin Skywalker of the OT where he was a contemporary of Obi-wan, a relic of a bygone age.
The right question here is whether or not the prequels are wrong, since their continuity is contingent on the OT, and in this case it’s pretty clear that they contradict the established canon of the OT.