Obviously, catholicism is the true form of christianity, which makes the most logical sense, its the OG christianity, thats why, the original.
How do you know that Catholicism is any more legitimate, true or OG than Orthodox Christianity, or any of the so-called heresies declared as such by the Nicean Council, or Judaism or Gnostic Christianity?
From the Orthodox perspective they are as OG as Catholicism once was, and it was Rome that went astray. From the heretic view, it was Nicea that exerted undue political pressure. From the Judaic, Christianity itself is a mistake. From the Gnostic, Pauline Christianity is just misguided.
To even decide that there ever was or still is a true, "OG" form of Christianity, you have to first make several arbitrary decisions. You have to decide that Christianity should not have remained a part of Judaism; that either Paul or the early Gnostics must have been correct; and whether, why and which among the several Pauline Christianity Churches that exist today is somehow deserving of being called "OG" despite Paul himself pretty much saying that his view was an innovation.