I just quoted to you the catechism that states ALL authority for salvation comes through the RCC. Re Read the bold sections.
It says through, based upon Scripture and the words of Our Lord. Not by, as you intimated. Re read the Gospels for further illumination.
The Church claims nothing for herself that was not given to her by Christ.
In John Jesus says, “As the Father sent me, so I send you.”
God, through His Son Jesus has established His Church which is guided by the Holy Spirit.
He made this choice so that all people could hear and know of Jesus and come to believe in Him and be saved.
Everything anyone knows about Jesus came to them through the Church, His Church.
The Church has been ENTRUSTED with the fullness of His grace and truth to the extent that God wishes it to be.
Yes, ALL of it comes through the Church by the will of God.