Dionysius was a scholar, a keen student of pagan as well as Christian learning.
Faced with the rise of certain dissident theological views in his diocese, he proceeded, not by excommunication, but by challenging his opponents to a public debate, with the thirty of them on one side and himself on the other. The debate lasted three days, by the end of which time he had talked all thirty of his opponents round to his side.
Only a few of his considerable writings have survived. One detail that I have encountered in a Bible commentary is his judgement that the book of Revelation had a different author from the Gospel of John, a view which he based on differences in the style of writing and other internal evidence. (The reader is reminded that the writer of the book of Revelation tells us that his name is John, but not that he is the Apostle of that name, so that Dionysius cannot be said to be contradicting the Bible.)