For the record, the issue is slightly different than Paul failing to mention earthly Jesus. Paul does not seem to be aware of a distinction between his own Apostleship and that of the original disciples of Jesus!
http://jesuspuzzle.humanists.net/supp06.htm
In 1 Corinthians 9:1 Paul asks plaintively: “Am I not an apostle? Did I not see Jesus our Lord?” It would seem that for Paul the mark of the true apostle is the reception of the proper visionary revelation and authority from God. In 2 Corinthians 10 to 12, Paul defends his apostleship and compares himself to unnamed rivals (they are not from the Jerusalem group) who are competing for the Corinthians’ allegiance: “Someone is convinced, is he, that he belongs to Christ? Let him think again, and reflect that we belong to Christ as much as he does” (10:7). And he goes on in 11:4 to reveal the source of all these competing messages and claims to legitimacy:
For if someone comes who proclaims another Jesus . . . if you receive a spirit different from the spirit already given to you, or a gospel different from the gospel you have already accepted . . .
Paul operates in a world of perceived revelation from God, populated by self-appointed apostles who learn about the Christ, and formulate their own interpretations of him, through the Spirit.
In all of his arguments over the legitimacy of his position, Paul never addresses the issue in this way: “Yes, I know others were appointed by Jesus in his earthly ministry, but the way in which I was called is just as worthy . . .” Had there been such a thing as appointment by Jesus, can we believe that this, or a link to those who had been so appointed, would not be the ever-present benchmark by which all apostles were measured? Could Paul possibly have ignored such a standard throughout the debates in which he engages concerning apostolic legitimacy? In fact, Paul’s arguments reject the very idea that there could be any deficiency of qualification on his part. And the implication of 1 Corinthians 9:1 is that, since his “seeing” of the Lord is to be regarded as legitimizing his apostleship and this “seeing” was entirely visionary, the legitimacy of the others he is comparing himself to, which includes the Jerusalem apostles, is based on the same measure, namely visionary revelation.
If I may ask, why is the issue of Jesus’ historicity important to you? To be honest, it makes little difference to me whether Jesus was historical or not. I’m leaning (relatively strongly) towards him being a mythical figure that was later historisized. If I’m proven wrong, and if Jesus truly was historical, this will not shatter my worldview. What about you? If Jesus was a myth, what kind of an effect will it have on your worldview?