Just to be fair, they compare every congressperson who becomes a leader with a “regular” (non-leader) congressperson who entered Congress in the same year and is from the same political party. Alternative view: people who becomes leaders are just more capable and better at selecting stocks?
The very first sentence of the linked article contradicts your alternative theory. These leaders performed similarly to their peers before ascending to leadership.
> we find that lawmakers who later ascend to leadership positions perform similarly to matched peers beforehand but outperform them by 47 percentage points annually after ascension
If what you’re positing were true wouldn’t they have outperformed their peers before ascension as well