In this article we first set out what complexity theory is and its place in economics. We then discuss whether complexity economics has observably transformed the mainstream before asking, even if complexity economics did in fact succeed in changing the mainstream, would this make the mainstream significantly different? The purpose of the article is to establish that complexity economics is different than the previously existing mainstream but, drawing on critical realism and social ontology, not as different as one might think. We conclude by suggesting there is scope for a more ontologically nuanced understanding of complexity.