Thank you for taking the time to write a thoughtful post.
I am not asking for historical proof beyond a reasonable doubt, although that might not be such a bad thing to do, if such were even possible, with respect to adherence to dogmas with anathemas attached to them. I am asking for reliable, historical evidence for a dogma that entails historical claims about a putative event in history
I am not asking for theological reasons or justifications of the dogma. It seems to me reasonable that claims about actual historical events should be backed up with some sort of reliable account of individuals who were personally present, or else were in contact with the events through unimpeachable sources, as is the case with the New Testament. Instead the only known source (a theological redaction of earlier tales) by which the teaching is known to have entered the Church are spurious, pious forgeries and outright fabrication containing admitted absurdities written by heretics.
Development of doctrine is a related subject to this, but it's probably not worth going into at this point.
Cordially,
If I get well enough to go to church today or tomorrow, I'm going to tackle some of the friars before I get back to you. I have to think what I mean by the Assumption being historical.