The Dogma of the Assumption of Our Lady is a problem for Crossbro?
Why?
Since Our Lord chose her, He wouldn't abandon her. One follows the other.
Now, Crossbro does say it's not in scripture but scripture should be seen as meeting notes, incomplete notes taken after the fact. We have Sacred Scripture but the apparitions of Our Lord and Our Lady and Church Tradition have filled in the all too big holes of scripture. Even Sacred Scripture speaks of other acts and how they are not noted.
As for the early Church Fathers being unaware, that's the whole point of a revealed religion. Just like Our Lord revealed His desire for devotion to His Sacret Heart for a world gone cold, the early Church Fathers did not have this dogma revealed to them. The Holy Ghost is guiding the Holy Catholic Church, that doesn't mean that the Holy Ghost is guiding the Church, not necessarily revealing dogmas that are due for a later time.
While dying on the cross, Our Lord gave Our Lady to St. John - this was while she was alive and it certainly could not have been for simple living conditions, there it too too much admonitions in Jєωιѕн tradition for any widowed mother to be left to fend for herself. Our Lord's great gift to His Church was superior to any merely human act. This act was a precursor that one could safely see foresaw the Assumption of Our Lady body and soul into Heaven.
In all of our sacred tradition, it is Our Lady who guides souls and pleads on their behalf and even gains permission from Our Lord to allow them to return and make amends.
If a bunch of protestants want to besmirch Our Lady, that is due to the envy of protestantism. Since protestantism is just "me and my bible and what I say goes" then that person would be filled with rage or indifferentism toward Our Lady. She was chosen by Our Lord in a most personal way.
Crossbro, if someone thinks one of the Marian dogmas are wrong, they should view that as a symptom of a potentially deadly spiritual ailment and seek the advice and counsel of a Traditional Catholic priest. Once someone starts thinking they have permission to discard dogmas, then - as you asked - where does that lead?
---->An Act of Reparation is in order here.