The problem with this argument, about it not being in the earliest MSS, is that if you start taking out later additions and interpolations to the Gospel of John, where do you stop ?
I do wonder if the Org's motive is not purity or accuracy, but the same as that of those in the early Church who objected to the Pericope, because it challenged their misogynistic and paternalistic attitude to women, and their legalistic preferences. *
Scholars have highlighted many such changes as above, including the position of some verses as we now have them, and of course, the well known later addition by another hand, of Chapter 21, why do the Org. include that ?
The Gospel of John is somewhat of a mess, and should be looked upon as an uncompleted work in progress.
* That is the reason I rather like the story !