I'm not sure what to make of this study, and their wording is careful:

"After ascension, however, leaders outperform their matched peers by up to 47 percentage points per year"

They looked at the 20 congressional leaders from 1995 to 2021 that traded stocks. They found _up to_ a 47% outperformacnce per year.

It's not clear (without trudging through the data) what the average outperformance was (or if there was any).