The argument that Mary never sinned is totally not supported by any Scripture and is an argument from silence itself. it’s only supported by tradition, which is meaningless.
Just because a group of men get together and decide something and then claim that God directed them, doesn’t make it so. If the history of the Catholic church was above reproach, they MIGHT have some basis for making the claim of Godliness and being Spirit led. The history of the Catholic church precludes both.
If you don’t accept the Councils, then why do you trust the bible that was collated by these same men?