That's speculative, and there's no consensus for this. Redactions and alterations could easily have occurred after 90 CE as well.

You are right that the Redactions and alterations" probably date after 90 CE, but I'm not talking about "redactions and alterations." Rather, I'm speaking about the earliest layer of the Gospel of John.

No, some Johannine expects suspect that this is true, but I don't think you could support the claim that most do. This is not the conclusion of Raymond Brown, one of the most esteemed Johannine scholars, for instance

You say most scholars who specialize in John's Gospel don't - Charlesworth (2018) and Culpepper (2009) says most do - a blatant contradiction. Brown wrote in the 20th century, so is not relevant for the changing tide in scholarship that has occurred over the past 15 years I would say.

nor is the the conclusion of Barton, Ehrman, Keener, etc.

Keener says no such thing. In his essay "Historical Tradition in the Fourth Gospel's Depiction of the Baptist," in Jesus Research: The Gospel of John in Historical Inquiry, 2019: "If, as many scholar conclude, the Fourth Gospel offers an independent eyewitness tradition for the ministry of Jesus, we can expect that it will provide some genuine information not contained in the synoptics" (pp. 254).