I have only seen the abstract of this article so far. However, the abstract as usual does give away the plot since it states –
We provide direct evidence on the effect of financial expertise on investment outcomes by analyzing private portfolios of mutual fund managers. We find no evidence that financial experts make better investment decisions than peers: they do not outperform, do not diversify their risks better, and do not exhibit lower behavioral biases. Managers do much better in stocks for which they have an information advantage over other investors, i.e., stocks that are also held by their mutual funds. More experienced managers seem to be aware of the limitations to their investment skills as they increase their holdings of mutual fund-related stocks following poor performance of their portfolios. Our results suggest that there are limits to the value added by financial expertise.
It also seems to imply that they only do better when they front run their own firm, a practice which if not illegal is immoral.