Not only oversimplifying, also misrepresenting. The council that Constantine had called was the Council of Nicaea and the members were all Christian bishops, Mithraism was not a topic .. if I'm reading your assertion right. At Nicaea, everything was not "up for grabs," the bishops were beholden to Holy Tradition and you can see the theological continuity before and after the council.
While Nicaea addressed scripture, the canon was not completely solidified for more than another 75 years. The scripture canon was not completely solidified at that point, but nearly so, the Old Testament in place as well as the tetraform Gospel and most of the epistles.
Normative belief was also fairly well established. The main topic was Christology and the Arian controversy, the Immaculate Conception was not a topic. But in the end, the Nicene symbol and canons that excluded Arian theology and asserted the Trinity were voted for 322-3.
And though many people on the internet like to say so, Constantine did not make the Roman Empire Christian. It remained largely pagan - though certainly increasingly Christian - throughout his rule. It wasn't until Theodosius in 380 that Christianity became the state religion. His personaly adoption of Christianity was not a means to unify his empire, it was actually a threat to the unity of his empire.
no subject
While Nicaea addressed scripture, the canon was not completely solidified for more than another 75 years. The scripture canon was not completely solidified at that point, but nearly so, the Old Testament in place as well as the tetraform Gospel and most of the epistles.
Normative belief was also fairly well established. The main topic was Christology and the Arian controversy, the Immaculate Conception was not a topic. But in the end, the Nicene symbol and canons that excluded Arian theology and asserted the Trinity were voted for 322-3.
And though many people on the internet like to say so, Constantine did not make the Roman Empire Christian. It remained largely pagan - though certainly increasingly Christian - throughout his rule. It wasn't until Theodosius in 380 that Christianity became the state religion. His personaly adoption of Christianity was not a means to unify his empire, it was actually a threat to the unity of his empire.