I'm not sure about Giuseppe's 'evidence' or reasoning in the OP, but one thing that might support the premise in the question, "Is the denial of Peter Mythicist evidence?", is Galatians 2:9 where shade seems to be thrown at James, Cephas and John as pillars, -
(ESV)
and when James and Cephas and John, who seemed to be pillars, perceived the grace that was given to me, they gave the right hand of fellowship to Barnabas and me, that we should go to the Gentiles and they to the circumcised.
The wording in the Greek is οἱ δοκοῦντες στύλοι εἶναι with
δοκοῦντες, dokountes, having the root,
δοκέω, dokeó, and δοκοῦντες being rendered variably from, as in the ESV above, 'seemed to be', to 'reputed to be', 'recognised as', 'acknowledged to be', 'esteemed to be', or perhaps even 'appeared to be', (+/- other variations).
- 'appeared to be' raises the prospect of 'appeared [as]' ...
Some version of Galatians 2 throw shade on the James, Cephas, and John a few verses before 2:9. eg., -
(ESV)
1 Then after fourteen years I went up again to Jerusalem with Barnabas, taking Titus along with me. 2 I went up because of a revelation and set before them (though privately before those who seemed/esteemed - δοκοῦσιν, dokousin - influential) the gospel that I proclaim among the Gentiles, in order to make sure I was not running or had not run in vain. 3 But even Titus, who was with me, was not forced to be circumcised, though he was a Greek. 4 Yet because of false brothers secretly brought in—who slipped in to spy out our freedom that we have in Christ Jesus, so that they might bring us into slavery— 5 to them we did not yield in submission even for a moment, so that the truth of the gospel might be preserved for you. 6 And from those who seemed to be - δοκούντων - influential (what they were makes no difference to me; God shows no partiality)—those, I say, who seemed - δοκοῦντες - influential added nothing to me. 7 On the contrary, when they saw that I had been entrusted with the gospel to the uncircumcised, just as Peter had been entrusted with the gospel to the circumcised 8 (for he who worked through Peter for his apostolic ministry to the circumcised worked also through me for mine to the Gentiles), 9 and when James and Cephas and John, who seemed to be - δοκοῦντες - pillars, perceived the grace that was given to me, they gave the right hand of fellowship to Barnabas and me, that we should go to the Gentiles and they to the circumcised. 10 Only, they asked us to remember the poor, the very thing I was eager to do.
note the 3 different versions of the word in
the Greek in vv. 2, 6 (twice!), and 9
And of course there's then the infamous confrontation -
11 But when Cephas came to Antioch, I opposed him to his face, because he stood condemned