St. Constantine was a Roman emperior and as such he lead numerous wars, including the one against Maxentius, a fellow Roman nobleman who was in rebellion. He converted to Christianity after he received the vision Eusebius describes. Maxentius was not an Arian and the war on him was not a war on the Arians. You knew that, didn’t you?
and you know that if Constantine had lost that military battle, he would not have been emperor and would not have been in a position to legalize Christianity.
And then the church would have been in a weaker position in its fight against arianism. Much weaker.
It was 312 AD that Constantine won the military battle.
It was 318 AD that Arius began his heretical movement.
One of my points is that all of that was happening at the same time.