Wesley was trying hard to be a calvinist in the tradition of Arminius.
Arminius was, of course, a professor at a major calvinist university and a preacher in a major calvinist pulpit.
He was examined many times and allowed to remain, and it was not until after his death that he was found theologically wanting.
My own sense was that he had a more expansive view of what Calvin taught and was able to explain it in person, but that his followers were not.
Two points there: Calvin was not a Calvinist; Wesley was not a Wesleyan. Goes with the territory. When great men are dead, their followers tend to get off the track they laid down. They simply don't have the same charisma.