The Catholic Church has always believed that Jesus Christ is the one mediator between God and man. It is the death and resurrection of Jesus alone by which people are saved.Look closely at what 1 Timothy 2:5 really says: Jesus is the only mediator between God and man. Because Jesus was the God-Man, only he can be the Mediator, the one who is between. Between men and the Father, there is the Son. This doesnt undercut our belief that the saints in heaven intercede for us because these saints, too, are (wo)men; they are members of mankind. Thus, we ((wo)men) ask them ((wo)men, too) to pray to the one Mediator (Jesus) in order to find favor with the Father.
In 449 Pope Leo the Great wrote his Tome against Eutyches, who taught that Jesus Christ had only one nature, not two. (This was the heresy of monophysitism.) In the Tome, which the Council of Chalcedon accepted as the authentic Catholic teaching on Christ, he quotes 1 Timothy 2:5 as the authentic Catholic doctrine: "Hence, as was suitable for the alleviation of our distress, one and the same mediator between God and men, himself man, Christ Jesus, was both mortal and immortal under different.aspects."
The fifth session of the Council of Trent (1546) laid out the belief in Jesus the one true mediator as the norm of Catholic faith: "[Original sin cannot be] taken away through the powers of human nature or through a remedy other than the merit of the one mediator, our Lord Jesus Christ, who reconciled us to God in his blood, having become our justice, and sanctification, and redemption."
The schema of the Dogmatic Constitution on the Principal Mysteries of the Faith, drafted for the First Vatican Council (1869-1870), includes the unique mediation of Jesus Christ as one of these principal mysteries: "Truly, therefore, Christ Jesus is mediator between God and man, one man dying for all; he made satisfaction to the divine justice for us, and he erased the handwriting that was against us. Despoiling principalities and powers, he brought us from our longstanding slavery into the freedom of sons."
Except for your last paragraph, you are agreeing with the content of Post #1, to which I also concur.