I do think the Episcopalian notion might be the most problematic. On the one hand, (some) Episcopalians argue for Baptismal Regeneration, the Real Presence, meaningful sacerdotal absolution, that kind of thing, while at the same time officially saying, "We could be wrong about this," both in the "Articles of Religion" (whatever authority they may or may not have) and in their toleration of clergy who deny Baptismal Regeneration, The Real Presence, meaningful absolution, and even the efficacy of prayer.
So it comes down to some of them saying,"When I pronounce you forgiven, you are forgiven ... uh, or not, maybe."
I think more capital 'P' Protestants would not believe any of that kind of thing and are franker about saying, "As far as I can tell, this is true and that isn't but, really, it's between you and God to work out who's right."
There may be a boat load of Protestant clergy who are weak in their faith, just as there, doubtless, are a boat load of Roman Catholic clergy with that same weakness; but it doesn't stem from the fallibility of Scripture.
In a nutshell, the orthodox Protestant belief is that Scripture is infallible and any doctrine which is in conflict with Scripture is fallible. That doesn't require all Christians to share all doctrine, merely that doctrine which is in conflict with Scripture be rejected.