We have a canon of scripture, which I accept, so you can dispense with arguments concerning how it is we’ve come to have the canon that we have.
I recognize your “white flag” and accept it. You accept - believe in - a core Christian belief not found in Scripture.
Moving on, the authority of scripture determines what is to be believed by the faithful.
Except for the canon of Scripture, in which you believe.
Christ, Himself states that in Mk 7:6-13, in which, He begins with a quote Isaiah, in which it is stated that those who teach precepts that invalidate the word of God, worship God in vain.
Let’s see what Mark says:
6 And He said to them, "Rightly did Isaiah prophesy of you hypocrites, as it is written:
'THIS PEOPLE HONORS ME WITH THEIR LIPS,
BUT THEIR HEART IS FAR AWAY FROM ME.
7 ‘BUT IN VAIN DO THEY WORSHIP ME,
TEACHING AS DOCTRINES THE PRECEPTS OF MEN.’
8 “Neglecting the commandment of God, you hold to the tradition of men.”
9 He was also saying to them, "You are experts at setting aside the commandment of God in order to keep your tradition.
10 “For Moses said, ‘HONOR YOUR FATHER AND YOUR MOTHER’; and, ‘HE WHO SPEAKS EVIL OF FATHER OR MOTHER, IS TO BE PUT TO DEATH’;
11 but you say, ‘If a man says to his father or his mother, whatever I have that would help you is Corban (that is to say, given to God),’
12 you no longer permit him to do anything for his father or his mother;
13 thus invalidating the word of God by your tradition which you have handed down; and you do many things such as that.”
I trust in your intellectual honesty to admit that Christ was not condemning all tradition and to provide the Scripture references that support the use of Apostolic Tradition; I need not, then, take the time to do so.
I further trust your intellectual honesty to admit you are equating “the word of God” with “the written word of God” which limits and distorts the meaning of the text.
Here’s another quote from Isaiah concerning the authority and preeminence of the revelation:Isaiah 8:20
To the law and to the testimony! If they do not speak according to this word, it is because they have no light in them.If what’s being taught is not according to the testimony, it’s not binding on the faithful—the canon is the testimony, and therefore, it’s only what’s taught in the canon that’s binding.
Again, I trust you to admit you are equating"this word" with “this written word” which is clearly neither stated nor implied by Is 8:20.
To take Is 8 as you wish us to, we must accept only the book of Isaiah, or, based upon the argument, the OT; but according to Is 8, the NT is out of the picture.

Belief in the assumption of Mary, IMO, is, according to the Lord, “worshipping God in vain” (Mk 7:7).
Better stated:
Belief in the assumption of Mary, IMO, is, according to Sandusky, “worshipping God in vain”