Wow, a lot to unpack here. I will ignore the US centricity.

The idea that people and parties don't somehow interact and in part align is absurd. Besides that parties have working groups and experts for various topics, it is only a special brand of persons who think they can alone in their chamber create better outcome than if they would speak to affected people and experts.

Besides that being in a party means that you are part of a multi faction battle within the party, this means you can asses how a person acts and who they align with (same is true in regards to not being part of opponent parties).

Then plenty of city councils and mayors are quite relevant, even in the small a lot of decision can fuck some people over quite a bit. To further my point you have to deliver some data though, which region are you living in / which region are you talking about when you mean city councils / majors etc. don't matter.

Finally especially in the small big economic issues matter. However in many local elections the two parties lead to results that are bad for workers, marginalized etc. since the parties are right centrists and don't really care how to better the lives for those and how to keep our planet alive. Which would need a switch from the capitalist imperial hegemony we got now.

For more inspiration do go and talk with people from Rojava and read up on Jineology as example.