You have a very important observation in the Australian system including sitting members who are not directly elected.  Everyone has to remember that "PR" does not represent only one model of alternative government.  There are at least 3 models of PR I can think of: MMR, Ranked Ballot and Assigned Proportional Representation.  There's not enough space in this comments forum to explain them all, so I'll leave it to readers to educate themselves on each.

What you're talking about is MMR, which I disagree with entirely.  MMR has got to be the least democratic form of PR ever conceived and has already been rejected in previous Canadian Provincial referenda.