If Constantine wanted to dominate the church, the obvious thing for him to do would be to try to widen the divisions in the church and keep them competing with each other.

That’s not what he did. Instead of “divide and conquer,” he did his best to unite the church, often against the inclinations of the bishops. Drake points ou that by devoting “considerable personal resources to achieving Christian consensus,” Constantine “weakened considerably his own capacity for independent action - his own, and that of his successors.”

Ultimately, his policy (conscious or no) was not “divide and conquer” but “unite and submit.”