I don't know if his numbers are right,,or not.
The problem is..the Congressman that are there for 20-30-40 years...Because THEY are in control. THEY tell the newbies what to do..and how to do it.
There may well be a big 40% or so turnover....
But THAT doesn't matter....if 40-50-60% of those in Congress have been there...20-30-40 years...and are pulling the strings.
Congressional incumbents have like a 90% win rate in primaries. They are there as long as they want basically.