Ok heres my take... Vader was caught by surprise by Luke who, with temporary dark-side strength, overcame his father and brought him to the point of submission.No, no. Vader was beaten before he made that choice. Luke's amateurish hacking away with his lightsaber should have been a cakewalk for any half trained Jedi to fend off. Essentially the problem with that sequence is that the filmmakers did not choreograph a decent fight sequence that could equal or outdo the one in TPM. That's one of the problems with shooting a series out of order. Vader appears quite inept when he shouldn't be. In theory Vader probably could wipe Maul off the face of the galaxy, but in practice, as filmed, the evidence is to the contrary.
Although inelegant, that final part of the duel was a very powerful scene. It was just pure strength and willing (on Luke's part).
TPM was a little different (and visually superb)... but that was then and this is now - or whatever...............
As much I enjoyed the 3 way duel in TPM... Nothing can take away the sheer anger and power of Vader's defeat.