Political scientists are generally focused on national governments and/or international organizations. To paraphrase a well known economist and political commentator, modern governments are essentially insurance companies with their own militaries. Add on a wealth redistribution function, and it's easy to see why competent national governments mostly behave alike, regardless of the policy positions of the ruling party.

My feeling is that this changes dramatically when you look at local politics, which is where most of the interesting action is. There's not much that the French government can do that, when zoomed out, is fundamentally different from Germany or Spain. There's a lot more leeway when you compare Tokyo or Shanghai with Mexico City.