Paul condemned himself too.
Peter was still the head of the apostles.
Paul makes the case for his apostleship vis a vis Peter’s by highlighting the impartiality of God (never mind Rome!). “Those men”—including Peter—”added nothing” to Paul. In fact they gave him the right hand of fellowship. The other apostles—including Peter—were those “who seemed to be pillars”. God is no respecter of persons!
You people strain out a gnat and swallow a camel...