Ballotpedia has analyzed the primary election returns from August 7. See here. In Kansas, 34% of all incumbent legislators running for re-election who had primary opponents were defeated. Kansas has closed primaries.
In Michigan, which has an open primary, 14% of all legislative incumbents running for re-election who had opponents were defeated. In Missouri, which also has an open primary, 23% of the legislative incumbents running for re-election who had opponents were defeated.
But in Washington state, which has a top-two primary, not a single legislative incumbent was defeated for re-election. These results confirm earlier research that no system is kinder to incumbents running for re-election than top-two systems. In California’s top-two primary in June this year, no incumbents were defeated. Thanks to Eric O’Keefe for the link.