I think it is a mistake to try to separate Scripture from Holy Tradition and the Magesterium of the Church. God is three Divine Persons in one. God’s Word, likewise, has a trinitarian nature. Just like we cannot separate the three Persons of God from the unity of God, we cannot separate the Scriptures from Holy Tradition or the Magesterium. All three must go together in a unified whole.
Jesus, Son of God, became man. He preached and taught His truth orally and by example. He never wrote anything down, and as far as we can tell, never told anyone else to write anything down. He did, however, command the Apostles (and by logical extension, their successors) to go forth and preach and teach everything He had taught them. (see Matt. 28:20) SOME of what He taught them got written down. We call that the New Testament. But not all of what He did and taught was written down (see John 21:25).
If we allowed every man, woman, and child to read and self-interpret the Scriptures, we would end up with what Protestant Christianity has become, an incredibly splintered, dis-unified, disagreeing mess, where no one has any authority to correct anyone else. Everyone’s opinion as to what Scripture says is as valid as anyone else’s. Why would anyone believe that Jesus intended to found His Church and spread His truth via a book available to be self-interpreted? He knew human nature was such that we’d end up with as many opinions as we have people reading and interpreting.
Jesus founded a (one) Church, which has been around for 2000 years. He sent the Holy Spirit to lead it into all truth, and which 1 Tim 3:15 says is the “pillar and foundation of truth” when it comes to doctrine. The Catholic Church does not, nor has it ever, claimed the right to correct Jesus Christ, or change the deposit of faith which He handed to the Church through the Apostles and their successors. All the Church can do is hand on what it was given. Period. And it has done so faithfully, for 2000 years now.