I would phrase it that he's taking an aggregate after applying a mapping which is (effectively) de-weighting the higher/positive returns. If he did the mapping

I would phrase it that he's taking an aggregate after applying a mapping which is (effectively) de-weighting the higher/positive returns. If he did the mapping (took the IRR) after doing the aggregate, it would be fine and would be what my intuition said which is that mean return doesn't depend on number of deals. You want to do the mapping to figure out how it compares to other alternatives that work on different time scales. But to do the mapping first warps the results and makes it seem like angel investing is a losing proposition without volume. Its not, its just a high variance proposition.