alt Hacker NewsAccording to this link [1] 200k would put someone above the 80th percentile and not far below the 95th percentile in terms of household income for the DC metro area, so I don't see how that could be considered "underpaid", especially when you consider the benefits.
[1] https://statisticalatlas.com/metro-area/District-of-Columbia...
The type of person who gets elected to Congress is likely to be far above average in charisma/intelligence/skill, and hence underpaid relative to what they could attain in the private sector