i think the answer is US style “open” parties are an (inadequate) attempt to address the lack of choice in a two-party system and PR proponents intend stronger, more “closed” parties when free entry provides that choice. 1/

ideally you’d liberalize party internals at the same time you reform the electoral system, although the transition does merit thinking about. (perhaps the “legacy” parties should remain open membership and primary driven, while new parties organize as they see fit.) /fin