The only reason "heresy" is so terrible is precisely because Father Feeney was right.
If he was wrong, if baptism and the full Catholic truth aren't strictly necessary for heaven, then the whole thing is a paper tiger. Who cares about "heresy"? Truth becomes optional, God's commands don't really matter. You can get to heaven without the Catholic Faith, and without Baptism. None of it matters.
Yet here they are, loudly condemning "Feeneyism" as dangerous heresy while insisting you don't even need the truth to get to heaven. That contradiction is pretty glaring.