Although your point is correct that in California close elections, Republicans were net benefited by the third parties on the general election ballots, I respectfully disagree as to your broader argument that the jungle primary is harmful.
In California there are really three meaningful political movements. Moderate Democrats (for the moment the most powerful) and radical leftist Democrats and Republicans (who are probably evenly balanced). There is FAR MORE ideological and policy difference between the moderate Democrats and the radical leftist Democrats than there is between the moderate Democrats and the Republicans. Demographics assure that Republicans can be elected only in a steadily-shrinking number of inland, majority-white districts. Anyone who has an economic stake in California has a HUGE interest in helping moderate Democrats win and hold office in the coastal and Hispanic-plurality districts.
Kamala Harris won her seat before the jungle primary came in, but I am very confident that in the intervening three years, her temptation to do wildly left-wing things has been held in check knowing that she could end up facing in November a death-penalty-supporting Democrat federal prosecutor turned County Supervisor with a Hispanic surname rather than whatever dolt the California Republican Party is likely to put up.
You raise some good points. Athough it seems to me that many of the “moderate” Democrats that I’ve seen aren’t much better than their liberal opponents (Joe Baca comes immediately to mind).
And I misremembered the 2010 AG race— Harris indeed beat Cooley with a narrow plurality in a multi-candidate field, not in a one-on-one runoff (since the jungle primary didn’t start until 2012). I think that it’s unlikely that Cooley would have come within 5% of Harris, much less within less than 1%, in a one-on-one runoff.