In and of itself, I don't see that much to which I would strongly object in Jude's statement.
On the one hand, the Scriptures do endorse the Protestant contention of Sola Scriptura, the doctrine that the Bible Alone contains within itself all teaching necessary for a Finite Man to attain a perfectly-rightful (albeit Finite) understanding of the things of God:
On the other hand, however -- Jesus and His Apostles organized the Church as a Social and Presbyterically-supervised Organization, and the Scriptures themselves also reject the notion of a completely-individualistic approach to the reading and understanding of Scripture (For myself, Jude, I don't know if I can justify "a disbelief in the complete perspecuity of the Scriptures"; just to make the point, I suspect that the Scriptures were "completely perspicacious" to at least one Man, Jesus of Nazareth. However, I can certainly believe in any individual Fallen Man's propensity -- even once he is Redeemed -- to get things wrong from time to time) :
The notion that "two heads are better than one", is, we might say, enshrined in Scripture:
So God has ordained that we are supposed to understand God's Word as the only infallible rule of Faith; but God has also ordained that we are supposed to reason together, and with the help of an Under-Shepherd of Christ (i.e., a Presbyter).
The accumulation of this "Reasoning Together, under ordained Presbyters", over the centuries, constitutes the "Magisterium" -- and if you've ever taken Notes of a Pastor's Sermon, you're engaging in a Magisterial sort of practice. Nothing wrong with that; we're supposed to glean wisdom from those who have gone before us.
However, I think Jude probably would differ from the Romanists on at least three points:
Unless I am mistaken (and Jude, correct me if you disagree with any of those statements, but I'm fairly confident that you agree), that would place Jude soundly within the mainstream of Magisterial Protestantism -- and certainly no Romanist Trojan Horse within our gates (grin).
Best, OP
You're 95% right.
[T]he Scriptures do endorse the Protestant contention of Sola Scriptura, the doctrine that the Bible Alone contains within itself all teaching necessary for a Finite Man to attain a perfectly-rightful (albeit Finite) understanding of the things of God:
The phraseology I prefer is that the Bible, properly intepreted, is the only infallible rule of faith and of life.
can certainly believe in any individual Fallen Man's propensity -- even once he is Redeemed -- to get things wrong from time to time
Even the best of us - even titans of the Faith like St. Augustine or Thomas Aquinas - have a tendancy to prejudice our interpretations by projecting our own experiences against the words of the text. It is simply impossible to strip all that away.
Jude would reject the "one head is better than two" Papist approach to reading Scripture and the Magisterium, favoring instead the Presbyterian-Conciliar approach ordained in Scripture itself;.
I don't subscribe to Papal infallibility, but especially this current Pope has a lot of credibility with me. He seems to recognize the most serious threat to modern Christianity is secular post-modernism. So I'll listen to him, just like I'll listen to any church leader with whom I share my disagreements.
Jude would agree with John Knox that the Reformation generally, and Calvinism in particular, produced amongst Christendom "the best school of Christ since the Apostles", affirming the Protestant contention that the Reformation (warts and all) was indeed a Work of the Holy Spirit;
I agree with Reformed theology, and believe it to be the most accurate, but there are a lot of warts there - and the resulting schism is something to be lamented. It may have been necessary, but if so, it is like chemotherapy - a radical treatment that is in fact poisonous itself.
that the longer and more-universally a Creed or Confession has become accepted amongst Bible-believing Christians, any Magisterial Teaching is always subject to the possibility of proper revision or clarification under the "Constitutional" bar of Sola Scriptura
That's certainly true in the case of the later early church father's like Augustine, or the monastics like Aquinas. I would argue, however, that the Creeds and the early writings like the Didache are the lens through which the New Testament must be interpreted, because the canon was not crystallized until after they were written, and these were unquestionably orthodox. Those writings are binding authorities on the interpretation of the Scripture.