Yeah, that would have been pretty thrilling to say the least.
Technically we did get to see Darth Vader move like Anakin because Anakin was christened with his new Sith Lord title before his fate on Mustafar and reconstruction, but yeah, I do get your point. With the bulk of the old David Prowse costume during the original films and the need for someone of Ray Park-level martial arts knowledge to come in and perform acrobatic combat stunts I just don't think we were ever meant to see such fighting out of Vader in the OT.
Anyways, Lucas has repeatedly said that Darth Vader in the suit was a shadow of his former self....a cybernetic creation that did little more than keep the shattered and dismembered man inside alive. Combat was never meant to be Vader's strong suit inside the armor....his forte was supposed to be his skills with the Dark Side(choking people, levitating and throwing things, psychic impressions and visions)....those would be more than enough to help him win the day against most adversaries.