The RCC wasn't formed and organized until after 300 AD.
Well that's somewhat misleading. I would say the RCC as an institution came into being a lot later than that.
We did not see this elaborate hierarchy in the 1st century.
The hierarchy of laity, presbyter, bishop was in place by then. Same fundamental structure applies. The admin has grown, but then the world's a different place today.
Sorry, but I used to be catholic and we all prayed to Mary.
Then show me where in the catechism we are told to worship Mary?
You can't. It's your error, don't load it onto us.
No it's not.
She was made co-redeemer and co-mediator.
Well for a start she hasn't — that title has been proposed, discussed at length for the very reasons you raise, but as yet is not formally ratified.
The big problem is that the RCC works out its theological statements from a very strongly metaphysical background — and most people make assumptions based on ignorance.
It is absolutely insisted that the Theotokos is human, no more, no less. (Theosophy, for example, would make her a demigod.) A favourite question is: Who baptised Mary, and when? It's not in Scripture, and if she ain't baptised, she ain't gettin' in!
The Catholic faith, unlike the post-Reformation denominations, insist that man takes a part in his own salvation, it's not something that either does or does not happen, and about which he can do nothing.
Jesus saves, as the saying goes, but He doesn't coerce ... and in our eyes at least, he affords man the noble dignity of being able to say "I played my part".
In short, if Mary had said 'no' to the angel at the annunciation, then where would we be?
So we see Mary as being the first to accept Christ, to open her heart to Him, and to do as He wills — and this has profound metaphysical implications for man, for what she can do, we can do, because she is not different from us. I don't know any doctrine in the West that comes anywhere near it for its depth and precision.
Each and every Catholic is comediatrix and coredemptrix, but in saying that we understand that it is in and through Christ alone that we are saved.
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The apostles taught that Jesus Christ alone is the Mediator.
So do we, and so does she, in all the Marian visions recorded.
God bless
Thomas