You have done studies of this that I think it is important that all Christians do.
Constantine changed Christianity, Constantine is a man we need to get to know. There are copies of his letters that tell us what his goals were, and his main goal was to be a good emperor to Rome, but he also stated over and over that anything the Jews do we must not do for they are an evil people. Scripture tells us how we are to treat Jews, and we need to obey scripture, not Constantine. Genesis 12:3 teaches us that “I will bless those who bless you.” God will bless those who bless you [Israel].
Something else we need to be aware of as Christians is that before Constantine people with questions about God went to those closest to the men who had known Jesus or were trained by those men. After Constantine questions were answered by councils that said they looked to the Holy Spirit to answer questions. Often they decided based on such as being against Jews, not by scripture as the Holy Spirit bases all things on scripture and is never in disagreement with it. They could make personal decisions and tell Christians they were from God when they weren't from God.
If you don't believe the pope has the power to make decisions for God that isn't in scripture, then you don't believe these councils could make personal decisions and say they were from God.