Why do some people say that the Catholic Church was established by Constantine in the 3rd century?

By the 3rd century, the church was already highly structured and authority was in the hands of the bishops. But they were constantly fighting each other over "heresies". Constantine wanted one hierarchy so he could control the church. He called the Council of Nicea and told the bishops to get their act together, agree on one doctrine, and that was it. So we got the Nicene Creed "I believe in one god, the father almighty and in jesus his only begotten son, etc..." and the "official" canon of the books of the bible. The "catholic" church already existed, it was the only christian church at the time, all Constantin did was cut down on the dissension so that he could control it easier.