I’ve never liked “Obi-Wan had a second apprentice, one named Vader the other Anakin, both turn evil, and then one dies while the other secretly survives.
It feels awfully contrived, and distorts the meaning of the PT to benefit the plot twist in Empire. The PT is all about Anakin’s turn to the dark side as a parallel to Luke’s resistance to the dark side, and both are symbols of the galaxy - in the PT, the Republic falls to the Empire, in the OT, the Rebels resist the Empire.
Removing Anakin’s proper turn to evil is (imo) the equivalent of removing Luke standing up to the Emperor. Instead, we’d just show Vader rising and overthrowing the Emperor, leaving Luke’s story in limbo, until a plot twist in Episode 8 reveals Luke did the right thing. It doesn’t work. Likewise, adding a second apprentice even if to support Obi-Wan’s lie would be the equivalent of adding in a new character (Luke’s sister?) for the sole purpose of having us wonder who will redeem Vader.
Now, this is all implying Lucas’ vision of the PT. It could have been set from an entirely new character’s adventures / struggles and not Anakin, in which case maybe he could have showed up in the first film and then been seemingly killed. But as long as the trilogy is about Anakin’s fall or Obi-Wan’s failure, I don’t think you can thematically justify keeping the plot twist.
A good reason fanedits of the PT should be made with the intent of dampening the flaws/improving the strengths of the PT rather than ironing out the continuity between the two trilogies. Myths of old have internal inconsistencies, as do modern ones; we should embrace and work within that condition rather than fight against it.