I think both of you are right.

Lemonstein, It's quite obvious that the Prequel Trilogy is unique and different from the Original Trilogy, with new characters, locations, and plot that tells of a story that is very different than the original trilogy.

However, as Bingowings points out, this is not two trilogies, but a saga. Taking place in the same universe, with one story pulling it towards aa conclusion.

So by making the identity of Vader intentionally vague (without eliminating the fall of Anakin [He still turns to the Dark Side, just {seemingly} briefly]) we keep the Prequel trilogy valid while still preserving the ESB twist.

Anakin's fall is intact, the rise of Palpatine is intact, and the saga (as many of us so desire) becomes more streamlined, feeling less like an original and a prequel and more like one long story.

Also, the Emperor in TFU is Sam Witwer, the actor for Starkiller. I was surprised at how good his impersonation was.

Also additionally, the Executor scene would have to be the last scene of Episode three, making it appear as though this takes place sometime in the future and this is the reveal of Vader.