So it's always rather a waste of time to tell educated Catholics that their beliefs are un-Biblical simply because they are universally acknowledged to be both Biblical and extra-Biblical. The Bible and Sacred Tradition make up one single deposit of truth, which is the Faith handed down to us by the Apostles.
Some non-Catholics (I'm not saying this is you) seem to think Christ founded a Church for no articular purpose, with no particular authority, and with no visible existence or structure or process of succession and with no visible continuity through most of 20 centuries.
Fine. But that's not the Church in reality.
The Church in reality is so much bigger than that. It's big, huge. It has immense depth and breadth. It spans history, it spans the globe. You're part of it, whether you know it or not. It is a great communion of love, and it is all Christ's, to use a thousand images, His kingdom, His flock, His dragnet, His family, His body, His bride.
But our ideas of what the Church is, are so different.
(Though I was talking with a dearly loved and respected Baptist man just today, and we and we seemed to have very nearly he same ideas, strangely enough, so there's no tellin' ...)
But to the extent that we do not understand "Church" alike, to that extent we remain, it seems, largely incomprehensible to each other.
If we go extra-Biblical the door is wide open to other teachings. I cited Mormonism as one. They can make the same claim the RCC does in that their extra-Biblical "teachings" were handed down from the apostles as well.
Their claim that Christ appeared to the Indians in North America can no more be disputed, or substantiated, than the RCC claims regarding Mary.
See the danger when you go extra-Biblical?