(Shea’s broader point regards the falsity of the Mormon historical narrative about ancient Christian apostasy, which then renders the entire religion categorically “unnecessary.” This is a red herring: faith in either the Roman Catholic or Latter-day Saint construction of history is ultimately subjective—one narrative is not objectively more plausible than the other, despite what apologists or detractors on either side may say.)
This, as near as I can tell, is a concession that there is no basis whatsoever for the Mormon claim of a Great Apostasy. And yes, in fact, the Catholic claim is objectively more plausible because the history of the Church can be traced and there is no evidence whatever of some break in apostolic tradition. Is there evidence of sin? Sure. But so what?
Conversely, there is no evidence–none whatsoever–for the historical claims of Mormonism. So the attempt appears to be to take the whole discussion out of the realm of verifiable historical data and evacuate it to the realm of subjective “narratives”. This is, frankly, of a piece with the Mormon tendency to appeal to “burning in the breast” and other such subjective phenomena as “evidence” for the “truth” of Mormon claims. It’s a curiously post-modern way of arguing. A sort of hyper-fideism that seems to me to despair the use of the intellect in evaluating any historical claim.
One of the many schisms of our time is the schism between faith and reason. Fideism such as the sample above (and a lot of Mormon apologetics) cancels reason and demands faith alone, while a lot of atheist agitprop cancels faith and worships reason (though it seldom uses it).
Meanwhile, here is Fr. Robert Barron on the proper relationship of faith and reason: