What if perceived polarization is actually purification?

From ‘Without Moderates, This Place Will Be Almost Unworkable’ by Audrey Fahlberg and Harvest Prude.  The subtitle is Centrists in the House of Representatives continue their yearslong vanishing act.

Per data compiled by the Brookings Institute, the number of House members who carried districts won by a presidential candidate from the other party—known as “crossover districts”—averaged well over 100 members for the 40-year period beginning in 1956. That number has shrunk every presidential election cycle since 1984, when 190 members—or 43.7 percent of the House’s 435 members—were elected in crossover districts. In 2020, that number fell to 16—just 4 percent of the entire lower chamber, per FiveThirtyEight’s Geoffrey Skelley. 

Democrats have experienced the trend more over the past two decades. “As recently as 2008, there were almost 50 Democrats who won the districts that John McCain carried for president,” said Sabato’s Crystal Ball election analyst Kyle Kondik, down from 86 in 2000. “In this most recent election, there were only seven [crossover Democrats]. Redistricting will sort of shuffle those numbers a little bit, but you’re just seeing a decline really on both sides of members being able to hold these districts that aren’t otherwise favorable to their party.” 

That's information I have not seen elsewhere.  What does it mean?  Fahlberg and Prude emphasize polarization and the importance of moderates in the system.  Maybe.  But I wonder.

I have long been in favor of one party having the White House while the other controls Congress.  That sort of split in power is a reasonable check-and-balance.  I have not particularly focused on the equivalent at the Congressional level before, the potential importance of cross-over districts, but it would seem to potentially serve a similar check-and-balance function.  I am thinking that while a Congressman wants to stay aligned with their party, they also need to be aligned with their voters.  It forces the necessary trade-off thinking and bi-partisan legislative coalitions necessary to pass legislation.

At the same time, I am keeping in mind my sense that Congress has increasingly become sidelined in the past thirty years as more and more rule making occurs via more or less accountable agencies rather than through legislation.  

I wonder whether what is characterized as polarization isn't really purification.  One would think that it is a good thing if, increasingly, Congressmen are indeed aligned with their voters (i.e. assuming that a vote for president is an adequate proxy for core values.)  

But if it is purification, then indeed, there are fewer of those in the middle with a real challenge when considering what the party wants versus what the voters want.