The questions you ask reveal a predetermined position that God is weak and needful of sinful people - of which ALL popes and bishops and the virgin Mary are counted as members. You ask me to explain why God does this or that? It’s a fools errand to put words in the Lord’s mouth - which is the job of the RCC and its Magisterium. The Apostles - of which Peter was not the leader, much less a pope - were of that time for the purpose of establishing the church. Contrary to the RCC and the non-RCC New Apostolic Reformation, there’s not a scrap of Scripture that supports the notion that the office of Apostle was used or meant to be one of multiple church rulership or authoritarian exercise.
People are not powerless - they are powerless to save themselves or others, but not powerless in other things. The Scripture is explicit regarding the sovereignty of God and we must, therefore, determine that’s man’s “free will” is something less.
Saints are chosen by God, saved by God, and kept until the day of judgment by God. The whim of God is greater than the grandest designs of men - the Bible puts it like this, in 1 Cor 1:20 - 25 “Where is the wise? where is the scribe? where is the disputer of this world? hath not God made foolish the wisdom of this world? For after that in the wisdom of God the world by wisdom knew not God, it pleased God by the foolishness of preaching to save them that believe. For the Jews require a sign, and the Greeks seek after wisdom: But we preach Christ crucified, unto the Jews a stumblingblock, and unto the Greeks foolishness; But unto them which are called, both Jews and Greeks, Christ the power of God, and the wisdom of God. Because the foolishness of God is wiser than men; and the weakness of God is stronger than men.”
Our purpose, speaking of Christians, is to glorify God. We do this by our “good works” - which the Spirit leads us unto after we have been born again. For all deeds done “in the flesh” (before spiritual birth) are sin.
If God MUST be a direct cause in everything, and apparently is diminished through the use of intermediaries, then why is this so readily contradicted by the very existence of the self-same Scriptures you hold are the only source of Truth? If those sacred writers were inerrant through God's grace, how is it impossible for Peter and his successors to have a similar charism of infallibility under certain conditions? Can't God handle disputes about the meaning of His Scripture directly? If He can - and clearly He can - then why doesn't He, always and automatically? Don't say that He does through the Holy Spirit in the forum of the mind in each believer. To say this, and cite the opinions of all individual Christians as "evidence," is to say that the Holy Spirit is the Author of confusion. For no two believers, no matter how much they pore over Scripture and beg for God's enlightenment, agree on everything! Yet, if the Holy Spirit acts on each individual, they should. It does not diminish God's power to acknowledge that He uses the teaching office of His Church, which He endows with His grace-filled authority, to promulgate the authentic meaning of His teaching.
Left to our own devices, we will talk past each other till the Crack of Doom. Since you deny the teaching office and authority of the Church which compiled, vetted and canonized the very Scriptures you claim to revere so much (in spite of the utter lack of logic in doing so), your house is simply built on sand. Since you likewise deny Christ's establishment of His ordinary means of salvation through His Sacraments, your own salvation, while hardly impossible (since, for us Catholics, it is a fundamental principle that nothing is impossible for God), is far more imperiled than you know. May God grant you the grace to see His Truth as He would have it seen.