You have asked multiple questions. First off when Christ said what He said about having foretold US all things HE was the proper authority. And it had already been penned by the chosen holy prophets that foretold US what would be. Even in Psalms 22 which Christ quoted while hanging upon that Cross.
Our Heavenly Father does not need us, we need Him and Christ is our 'vehicle' through which we were given to have access to the Heavenly Father. NOT any earthly organization that thinks they can make it up as they go along, or wrap in ancient traditions to increase the pew sitters.
Who has the power of attorney now?
Mt:28:18-20: "And Jesus came and spake unto them, saying, All power is given unto me in heaven and in earth. Mt:28:19: Go ye therefore, and teach all nations, baptizing them in the name of the Father, and of the Son, and of the Holy Ghost: Mt:28:20: Teaching them to observe all things whatsoever I have commanded you: and, lo, I am with you always, even unto the end of the world. Amen."
And the Bible tells us in John 21:25 that "And there are also many other things which Jesus did, the which, if they should be written every one, I suppose that even the world itself could not contain the books that should be written."
So if the Bible says that it does not contain everything that Jesus did, it is not a complete authority on its own.