Very interesting OP!
It reminds me of what an other user here made me realize:
The different books of the Bible and the Bible as a collection of books are the result of religion. They are not the basis for religion.
Like any other book that describes something, it cannot contain everything there is to know about the topic described.
You can't build New York based on a couple of books describing the city and it's culture.
Likewise, it's impossible to build a complete and true religion from the Bible alone.
Simple logic dictates either tradition or revelation are needed in addition to the writings.
Watchtower has neither, and doesn't even claim to have those either.
Watchtower is building New York from a book.