But if Peter was blamed because, after he had lived with Gentiles he separated himself from their companionship out of respect of persons (separabat personarum), that surely was a fault of behaviour, not of preaching. For no question was therein involved of any other God than the Creator, nor of any other Christ than He Who came from Mary, nor of any other hope than the resurrection.[Praescript. 23]
The idea seems to be here that Paul was orthodox insofar as he was the first to argue for a 'universal' Church.
Just previous to this the author puts forward Paul as arguing against the separation of the gospel
Afterwards, as he himself relates, he "went up to Jerusalem to see Peter," because of his office, and by right of course of an identical faith and preaching. For they would not have wondered at his having become a preacher from a persecutor if he had preached anything contrary to their teaching; nor would they have "glorified the Lord" if Paul had presented himself as His adversary. Accordingly they "gave him the right hand," the sign of concord and agreement, and arranged among themselves a distribution of office, not a division of the Gospel (non separationem euangelii), namely, that each should preach not a different message, but the same message to different persons, Peter to the Circumcision, Paul to the Gentiles.
Of course the language here is very reminiscent of the argument against the Marcionites in Irenaeus (i.e. that they wrongly 'separate' the gospel).
The sense seems to have been that both the Ebionites and Marcionites 'separated' the Church but that Paul was the ultimate spokesman for 'unity.' I am not sure this was historical accurate. I also think that large parts of Galatians (in chapters 1 and 2 especially) must have been falsified by Irenaeus to accomplish this caricature. Notice also that the author of the Praescriptionem (Irenaeus) denies the heresies claim that Paul praised the establishment of 'sects' (heresies):
Besides, when he rebukes dissensions and schisms which are undoubted evils, he immediately adds "heresies" also. That which he adjoins to evil things he assuredly confesses to be an evil, and indeed a greater evil, since he says he believed concerning their dissensions and schisms, because he knew that heresies moreover must be. He showed that in view of the greater evil he easily believed about the lighter evils: certainly not meaning that he thus believed concerning the evils, because heresies were good, but to forewarn them not to marvel about temptations of a worse char- acter, which, he asserted, tended to make manifest those who were approved, that is, those whom heresies could not pervert. Similarly, since the whole section savours of the preservation of unity and the restraint of divisions, whilst heresies divorce from unity no less than schisms and dissen- 'sions, undoubtedly he includes heresies in that same category of blame in which he also places schisms and dissensions; and hence he does make those to be approved who have turned aside to heresies, since he pointedly exhorts men to turn away from such, and teaches all to speak one thing and to be minded the selfsame way—an ideal which heresy does not allow. [Praescript. 5]
The heresies certainly would have laughed at the notion that Paul was a spokesman for one 'united' orthodox Church. But it is important to note that the Catholics had to co-opt Paul to 'call out' Peter for being captured by Judaizers.
The historical reality seems to be that the author was using Paul to appeal his message to former Judaizers. Marcionites were not embracing this message willingly. The aim was to say that Paul is the witness for Peter's change of mind - a curious argument given the repeated claim that the Judaizers hated Paul. I think the evidence when taken as a whole seems to be that the apostle hated by the original followers of Peter was not known as 'Paul'. (cf. Adv Haer 3.15, 16). My guess is that it is more likely that he was known as Mark (hence Tertullian's failure to cite from Mark in a critical section of De Resurrectione Carnis). Now Paul was recast as someone who didn't author a separate gospel (as the Marcionites claimed), who wasn't Mark. Mark is left in the darkness and this new figure of Paul comes into the light who - through the claims associated with the Pastorals - because the ultimate spokesman for orthodoxy and a united Church.
My suspicion would be that the original followers of Polycarp = kata Phrygians.
