but for me all the downballot third party candidates are eliminated in the primaries.

What do you mean? A primary would be where Democrats narrow their choices to one nominee, and Republicans do, and third parties do and so on. You seem to be suggesting that primaries filter out third party candidates? Maybe I’m just missing something but my understanding would be that a primary would just be a way that a third party chooses a single nominee, same as the first two parties.