Exactly my thinking, Scott.

A color copier has red, blue, yellow and black ink, and that's all we need to create full-color prints. Same for our political systems; if each of the four parties have equal chances to serve the public, then four parties is all we need.

For the State levels in the USA, my suggestion would be to use the German voting systen, which is the USA voting system but fixed up. They still vote in districts with a single winner, yet they also count all the votes in a State and fix up the outcome proportionally.

For instance, when a State has forty districts and therefore forty seats, and a party does not win any seats yet garners ten percent of the votes, then four seats are added to the total of seats, so the voters are represented fairly. This way, gerrymandering is a thing of the past because the shape of a district doesn't matter any longer.

The Germans did put a threshold in place that if a party does not have at least five percent of the votes, then they won't get any seats (unless they win a district, then they get that seat).

As a result, the German political system has about six parties. Just about right, more is not needed.

I've been told that US officials helped the Germans set up their voting system after WW II. They channeled the Founding Fathers, but then in a 20th century kind of way.

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Proportional is derived from pro-portion. A portion of the voters will get the same portion of the seats. Multi-seat is a variation and not as pure as regular proportional voting.

Scandinavian countries have multi-seat proportional voting. Yet what makes them stand out as well is that they have one House and one House only. No president, no senate. The voters are most-empowered therefore. Naturally, it helps that these nations are small nations. They don’t make decisions that shake the world. They’re ‘just’ examples of a good political society.