I don't think that is actually true. It is in part redistricting that lead to the ascendancy of extremism, by putting all of the strategic emphasis on the primaries in uncontested constituencies.
"Redistricting" isn't a new recent thing, it is a process done by state legislatures to state and federal legislative district every decade that has been used for both personal and partisan advantage since the founding; the word "gerrymander" was coined in criticism of a particular instance in 1812.
I think there is a primary-related problem going on right now that could change historically held positions on the value to financial backers interests of uncontested general elections.