Upvote:5
There is not as much disagreement over Jesus' appearance as your question indicates.
In fact there is near unanimity amongst Christians on the matter of his appearance - specifically virtually all Christians agree that we do not know what he looked like. The scriptures record nothing of his physical appearance, and there are no other authoritative descriptions of him. While various people have speculated on what the might have looked like, given the norms of his day, nobody outside the conspiracy-theory fringe claims to have any certainty.
Celsus was not a Christian, and wrote what he wrote as part of an attack on Christianity. He also lived 100 years after Christ, could have have seen him and was unlikely to have met anyone who did. Origen did not "agree" with Celsus, and most of what we know about Celsus comes from Origen's refutation of his thought, though it is also possible that Origen did not refute Celsus' accusations of 'ugliness', since it has never been important to Christian thought that Jesus was beautiful.
The quote you ascribe to "St John Chrysostom" is not actually from him, or any of the other church fathers, but from Archimandrite Nektarios Serfes (Boise, Idaho, USA January 2004), who gives a confusing series of nested quotes, some of which are drawn from St. Nicodemos the Hagiorite (1749-1809), who in turn partially quotes Chrysostom but makes it unclear where the Chrysostom quotes end. The parts that I have been able to attribute to Chrysostom are commenting on the "attractiveness" of Jesus being based on the good and miraculous works he was doing, not on his appearance.
The "letter of Publius Lentulus" is fictional and dates from the fifteenth century.
The majority of opinion (and it is opinion) is that Jesus probably looked neither very beautiful nor very ugly, making it easy for him to be "lost in the crowd", although many would put that down to supernatural intervention. Other questions on this site discuss the issue of Judas' identification of Jesus, and how it might have been necessary even if Jesus had a distinctive appearance.
To answer your actual question the lack of knowledge about the appearance of Jesus does not in any way cause doubt about his existence. It was perfectly normal in those days, when making a likeness of someone was a major undertaking and was done only for those at the absolute pinnacle of political importance, that nothing was known about the appearance of people who definitely existed. To my knowledge no record has survived of the appearance of many major figures from the time, but that does not cause us to doubt their existence.