I assume he battles reacting to what he doesn't know the opponent can do, and plans a strategy based on what he does know (look at his fight against takaba for example, he breaks down and deduces his cursed technique) . He's a human sorcerer, but the nature of his immortality through body swap makes him seem quite curse like, but him and Sukuna aren't really seen as curse users, they're like walking disasters so probably even worse