Omollo, like you I must claim underwhelment
First of all, having looked about, it appears this scholar does not at actually represent a consensus, as may appear, and that the volume he has written (in German) of which he provided the English summary that you have cited, is controversial and has been answered by other scholars, but in German, which I cannot access.
However, it appears to me his basic argument is that the Epistle/book of 1st Peter is "fictitious" and that the Epistle dates not from the 1st century but from the 2nd century long after Peter's death (this is just stated as established fact, no evidence in sight anywhere in the article, however) and then an emphatic interpretation of the reference to "Babylon" in that Epistle (again, simply stated as fact, evidence onge!) that does not match any of the uses of the term among Christians and Jews of the 1st/2nd century who per most scholars, as I understand it, used it to refer to the actual Rome...the empire/capital of the empire.
The rest is simply that (a) st. Ignatius' reference to Peter and Paul having special authority over the Roman church (110 AD) means something other than what has been taken traditionally to be the meaning (that Ignatius believed that Peter and Paul had a special relationship to the church located in Rome) or that (b) st Clement's letter (from 96/7 AD) again means something else. He admits to a christian tradition of the death of Peter by the Roman church but dates it to 150/160 AD. Of course, he does not bother to explain what would motivate the christians of this particular church to just invent such a tradition from whole clothe, and why the Palestinian churches (Jerusalem and Antich) where this author claims Peter lived and died and never left, would allow this rubbish without objection. Were they not aware of the death and burial of their own bishop and beloved apostle? Even granting that the tradition is first recorded in 150 and accepting his dismissal of 1st Peter, Clement and Igatius, that is still early enough that the churches knew Bishops/leaders who had known the apostles or the earliest apostolic fathers. That others would not have said, no, st Peter is burried at his church in Antioch/Jerusalem, just seems an amazing claim to make to me.
Everything else comes down to this: Its not written in the Bible (this after disparaging 1st Peter as fictitious and then giving an interpretation of Babylon that is unique and doesnt follow the use of the term among the Jews and christians of that era). Well, anyone who has read the New Testament knows that it doesnt mention all/detailed accounts of the lives of the apostles, apart from st Paul whom Acts follows extensively. From the New Testament, you can't know much of how most of the apostles lived and died in the 1st century after Jesus had left. That doesnt mean they vanished from the earth and didnt do anything else, live or die, its just not something that was recorded in the letters that were to form the canon of the new testament. However, a tradition of early christianity does exist and cannot be simply wished away. Neither is it contradicted by other christians, so it appears there is no "smoking gun" here at all. Just an alternative view of history, IMO. And a view that to me, simply doesnt make sense of all the evidence but is entirely a big old argument from silence.
