Well, I have seen two distinct ideas regarding the GA;
The first is the Structural Argument: The Apostles died before transmitting their keys as apostles to other Chirsitians, and therefore the Apostacy occured because of the loss of those “keys”. As evidence, those who argue this pov, point to the passages in the NT wherein the highest position mentioned is a bishop. The confusion is, a bishop under the RCC is a much higher (within the hierarchy of the Church) postion than in the LDS church, where it is the lowest of the higher callings, with the “position” of Apostle being higher than a bishop. Remeber, one of the things “restored” by JS was the actual hierarchical structure of the church. This argument for the GA is countered with the knowledge of the RCC that a Bishop was the highest on the old food chain ever established, and that apostles are not higher than bishps, and so simply show their preistly succession lines.
The second line of reasoning (and the apparent one being questioned in this thread) is more complex due to disagreement over what, precisely, doctrines changed; but simply put, the theologians of the early church began to change the doctrine as taught by Jesus, and thereby caused the GA (and therefore not necessarily through their sin, just their hubris; so even the “good” catholics contributed to the GA), because all of their Councils caused the “philosophies of man” to insert themselves over the actual teaching of God. I suppose, technically speaking; any doctrine of the RCC that is different from the “restored Gospel” of the CoJCoLDS would be the false doctrines introduced by the errant ECFs.
I do not see how these issues would remove authority from the faithful.
That is because you are Catholic. The RCC long ago came to the conclusion that the personal worthiness of a preisthood bearer did not alter the efficacy of the exersize of their preistly office. The LDS used to disagree. They took the Protestant view that a preist could lose the preisthood through immoral or unrighteous action (and technically this is still in the Standard Works, so it should still be a teaching of the LDS church).
Case in point: The RCC insists that ANYONE performing a Baptism, under the prescribed conditions (intent & formulae), can perform an effective and binding baptism. By contrast, the LDS assert that only baptisms performed under specific ritual by one with the preisthood given by the church can make a binding & effective baptism. Thus, one of those pagans in your Parish could, if needed, baptize someone as effectively as your bishop into the Church. The equivalent pagan at the local Ward, however, cannot baptize anyone unless they hold the actual preisthood, and are given the bishop’s leave. This is also why most christians baptized outside the RCC (like me) are still considered actual “baptized Christians”, even though not Catholics; and conversely, why everyone entering the LDS faith must be re-baptized.