It's no coincidence the MC transmigrated to become the Pig Duke. He does have the basic personality for it. A good example is the scene where he told Alice she's the one his past actions offended the most and he owes the greatest apology to. When she took such a serious sounding confession seriously, as anyone ought to take, he started mocking her. It must be how the original Slow the Pig treated Alice as well, always trying to provoke her for his own amusement, because she's indeed easy to provoke. So, yeah, the MC's soul was a good fit for Slow Denning.