You mean the absence of archeological evidence, don't you???
It's clearly a site that was venerated by Christians going back well before Constantine.
You mean venerated by "pagans", don't you, because the Vatican was built upon a pagan graveyard full of tombs of sorcerers and magicians.
It's kind of hard to spin graffiti reading Petros eni ("Peter is within").
The graffiti must be referring to "Peter rabbit" whose remains are there with a whole lot of other animals as the archeological evidence proved.
Oh, that's mature! Or is it manure? Consider the history. If Peter was executed as a common criminal, then he would be placed in a grave near the site. The Vatican was like Golgotha, outside the city walls. Since Christians were being executed right and left, his body would not have been taken to a more dignified tomb, as our Lord's was. And it has been almost two thousand years. But seriously, why do you think that Constantine built his basilica on Vatican Hill if it were not the reputed place of Peter's grave?