Exactly. It is possible without the list. The open or closed list actually allows for contagion effects where parties are influenced by, say, for example, smaller parties in the context of P.E.I. historically, that have nominated more women as candidates, but it hasn't translated into more women elected. Considering the list holistically, in the context of P.E.I., the 27 districts as a whole and considering perhaps gender, diversity, and geographic representation within that list, currently what happens is that nomination processes take place within silos. They happen independently of one another and you don't know what will happen until all 27 are nominated.
As you say, it is possible to have regulation, legislation that requires gender parity without a proportional system. It is possible.