LOL. This "historian" claims "impenetrable darkness" on Peter's succession but then goes on to admit there are numerous references to the line from wide ranging sources. After Peter was executed by Roman authorities, there were a series of short-lived successors who were executed amidst an environment of secrecy and disorder. With such a great volume of evidence on Peter's line, it is not surprising to find discrepancies that leave out or confuse some of the short and secretive reins.
Your post clearly demonstrates that nobody doubts the fact that Peter had successors.
Whether Saint Peter was succeeded by Saint Linus, then Saint Anacletus and then Saint Clement or if Peter was succeeded by Clement was moot because Clement was consecrated a bishop by Peter and the Apostolic Succession is intact from there.