Considering that it is the Roman Catholic canon the protestants took a hatchet to, I would say the protestant shouldn't even bring up other canons (EO, OO).
The 73 book canon has been consistent from the late 4th Century until present day. I believe
@Xeno.of.athens laid out the timeline very well.
It apparently counted for something in the 16th century. If it didn't count for anything, none of the 73 inspired books would have made it into the protestant Bible.
Whatever you bind on earth, shall be bounded in Heaven. Whatever you loose on earth shall be loose in Heaven. Jesus disagrees with you.
Thars is what is unique about Christ's Church, everyone is not their own authority.