The early church was comprised of many Jews. The Apostles etc. The Trinity is Divine Revelation, the nascent Catholic Church did not "come up with" it.
The doctrine of the Trinity isn't in the Bible. Jesus never claims to be the second person of the trinity, wholly equal to God. As a Jew, he would have found the whole concept offensive. Reread what he said in my reply #40. Note, he refers to the ONE God, as "OUR" God, meaning his God, too. One of the biggest obstacles in converting Jews and Muslims to Christianity, is the doctrine of the trinity. There is ONE God, not 3 in one.
You're right that the Catholic Church didn't "come up with it". Instead they borrowed it from numerous other Pagan sources. If you want me to list them, i will.