> A primary role of political parties has traditionally been to filter candidates. It's literally their raison d'etre

Yes, that's exactly why they shouldn't exist.

I don't know about that, but if they exist, they need to be stronger institutions that take more of an active role in picking/filtering candidates.

The introduction of the partisan primary has been an unmitigated disaster for our politics, by massively empowering the most zealous fringes within parties