What does that have to do with anything?
I'm sorry but that doesn't in the least clear up the fact that this "story" doesn't defend the fact that every single other visual depiction of John has him depicted in exactly the same way. DaVinci painted John in the Last supper the exact way every other artist before and after him does. As a rather feminate looking male close to Jesus.
Scotomisation doesn't enter in to it. The picture depicts what it depicts nothing more, nothing less. And it certainly doesn't depict Mary Magdalen next to Jesus. Take a look at the art from that timeframe and you will discover that the person in the painting looks like John and does not resemble any other depiction of Mary Magdalen available.