It actually does, if you believe that the people in leadership positions have been earning money for longer and have more experience in investing. You could also easily argue that they are more successful in general than congress people of similar tenure who aren't in leadership positions.

You are basically comparing the CEO to middle layer management, and then what do you expect? You need to do a more balanced comparison than that to show an actual discrepancy. Or maybe get congress to dole leadership positions out at random and then compare?

I’m not defending congressional trading, but there are potentially other confounding variables (emphasis on potential). Leaders may tend to be older, have more appetite for risk, or leadership may correlate with wealth/status because “the connected” can also raise more money etc etc. Unless those types of variables are controlled for, it should temper how strongly we draw conclusions.