It also means that people are voting for party lists, not individuals, and the lists are controlled by the parties. In a proper parliamentary system the parliamentarians directly represent their voters, and have a mandate from them. Parties do not have that, only MPs have that. By passing the mandate from the representative to the party, and the party having list control, that puts far too much power over parliamentarians in the hands of unelected party functionaries that draw up the lists and have no mandate themselves.

That's way less bad than it appears, because in a proportional system you will have more than 2 parties. In practice, every election is an election of those invisible bureaucratic hands, instead of some heads on display.