##What God could do =///= What God has done.
As matters have in fact been arranged, God has entrusted the salvation of the world to secondary causes, through which He always works. He is always at work - through them not least.
Some people's salvation will depend on the Bible - they may have no other means of knowing of God. Yet the Bible is less important than the Pope, because the Pope is made in the image of God, & the Bible is not. Abstractly speaking, the Bible is superfluous - this follows from your own reasoning. Why bother with a book, when God is so much better & more important ? Even Fundamentalists don't believe in salvation by the ink of Exodus, or justification by the grace of Acts 21. They believe - or say they believe - in Christ. If Catholics are idolaters, as Fundamentalists insist, Fundamentalists are Bibliolaters: they adore a book instead of the One to Whom it is meant to point. If Fundamentalists can get away with accusing Catholics of Pope-worship - Fundamentalists must expect to be accused of idolatry, such as Bible-worship. Make one accusation - & get one free.
There is so much wrong with the Bible anyway. Your reasoning against the Pope may rule him out; but it also rules out the Bible. Only inconsistency knocks out Pope, Bishops, Church, Doctrine & Sacraments, while sparing the Bible. The Bible is not a moral agent, so it cannot sin, unlike a person - but it is sinful in other ways: so by that analogy, objections to the ministers to God's ministers because of their sinfulness, are, if decisive, equally decisive against the Bible, which is a storehouse of sin. If the Bible is God, then it can't be ruled out. But only if it is God can it escape being a created means of grace. Are there Christians who think God is the Bible, & the Bible, God ? I don't know.