Yes, that's the mental block isn't it? That this is some form of novelty. You will find nothing in Scripture or in any of the apostolic writings which contradicts the dogma of the Immaculate Conception and you will find significant evidence to support it.
Firstly, the angel's salutation to Mary recorded in Luke's Gospel as "full of grace" is one such example, the term "full of grace" being understood to mean a unique, supernatural state of soul. The writings of Justin, Irenaeus, Cyril of Jerusalem among others of the early Church fathers all developed this theme and it has been addressed by many other saints of the Church down through the centuries.
“Anyone who runs ahead and does not continue in the teaching of Christ does not have God” - so, how far ahead do you have to get before you cease to be a true church?
The Catholic Church being built on the Rock, Peter and being the recipient of those promises given to Peter will never cease to be a true Church for it is the Mystical Body of Christ.
As always, these discussions inevitably founder on the issue of authority and the promises Christ made to His Church to keep it free from error.
Those promises do not apply to individuals of course, hence the quote you supplied refers to "anyone". Individuals have and continue to apostatize. The authority of the Church gives it the power to "bind and loose" as Christ promised Peter.
As for "how far ahead do you have to get before you cease to be a true Church", well there is only one true Church. "There is one God, one faith, one baptism" (Ephesians).
Ergo all Churches bar one are in error to some degree.
Nothing to contradict it except the verses saying all had sinned...
You also need to study the full of grace passage a bit harder...it means God had given her grace at some point (no idea how long is conveyed) and it still existed at the time the angel spoke. It did NOT in any way suggest she was always without sin, just as the same grammar in the previous verses didn’t indicate she had always been betrothed to Joseph!
The error of Catholics in reading about the church in the NT is to assume ‘church’ refers to the ecclesiastical structure that is the Catholic Church. That is why Thomas More was upset with Tyndale’s better translation of ‘congregation’ - it robbed Rome of authority. That is also why King James ordered it not to be used in the KJV - to protect the Anglican Church, which in turn protected his throne.
However, the NT church had congregations with deacons and elders. The Apostles, by their office, held a unique role over ANY congregation, and also in writing scripture.
Read Exodus 28-29 to see how God ordained the Aaronical Priesthood. Why be so specific about Aaron, and give nothing specific to Peter?