The fact that the same figure (John) became a judaizing icon for some Christians and a gentilizing icon for other Christians may be used as evidence of the fact that the name 'John' was merely another name candidate for the name of the Messiah, later supplanted by the name of Jesus.
For example, the gematria of 'Serpent' (I go to memory) is the same of "Messiah", hence you have a Jewish (gematrical) origin for the clearly gentile belief (Naassenes, Ophites, etc) that the Serpent was a positive figure against the evil demiurge YHWH.
I think that the same process went with the name 'John': the gematria allowed his identity with 'Messiah', hence, a Jewish origin for the claim, apparently not in contradiction with the gentile co-optation of John as the anti-YHWH hero of Mandeism.
Hence the 'fame' of John-Baptist is due solely to gematrical reason, just as the 'fame' of the Genesiac Serpent.
THAT is certain, whether in a Literary Setting (...as a Fictional Story written around the Passover of 4 BCE) or Real one (It actually happened and was reported by a Nicholas of Damascus or someone in the Priestly Groupings).