https://www.nber.org/system/files/working_papers/w26975/w269...
Both papers could be true if congresspeople are worse than the public at picking stocks, but congressional leaders are just better than the average congressperson
Real-estate investing is another corruption vector. One way to bribe a politician is to sell them a house at a million dollar discount. The optics become that the politician is a “savvy real-estate investor".
It could be possible that someone in Congress has insider information about a specific industry that helps them, but not about a specific stock. For example, if I knew about specific legislation that would impact auto manufacturers I may have a better idea to get in or out of that sector without necessarily knowing if Ford will do better than GM.
To your point about meta-analysis it would also be useful to know if members are worse than normies at picking industries as well.