The fact is that it is far truer than whatever beliefs you may hold, right?
After Constantine adopted Christianity, orthodox Christians like St. Athanasius of Alexandria found themselves persecuted by the Arians.
The monastic movement continued the fight against secular rule over the Church, etc.
Modern Evangelicalism simply DID NOT exist before Constantine.
The Eastern Orthodox monks have continued the tradition of resisting secular authority to this day. So you are oversimplifying things if you try to make it seem that Constantine changed Christian theology.
Ante-Nicene and Post-Nicene theology are much the same.
Do you reject the First Council of Nicaea?