New Zealand is vulnerable to it though: MMP makes it harder to form majorities, and encourages the election of "hacks" - abrasive party people who the system motivates to carve out a brand rather than inclusive electorate-centric members. This pattern also plays out in Gerrymandered electorate systems like California.
> The advantage is that parties like the Greens have a
> much fairer slice of the influence.
I understand your point, but disagree with a premise. The way you've stated that thinks in terms of party brand, rather than representatives.The Westminster system is fundamentally about responsible representatives for the purpose of governing. Members with electorates have an incentive to be mild and inclusive, to keep their electorate happy. Whereas parties have incentive to be abrasive to carve out brand. Electorate systems that favour parties have a jobs-for-the-boys culture.
Look at the US or Australian senate vs the lower houses. Or the UK upper house which is one of the most effective in the world for the purpose of performing quality review despite being not elected. It's also the only upper house I can think of that's not packed with teachers, lawyers and party hacks.
If anything, what we should be seeking is to reduce the reach of parties. For example, the Hare-Clarke system used in Tasmania doesn't have party names on the ballot papers and you're not allowed to hand out how-to-votes outside polling booths. (Tasmania multi-member electorates have a counter-effect to this though, and encourage party strength)
The continual pursuit of democracy for its own sake is not necessarily a positive force. Before the 1948 Australian senate reforms, the Australian senate was elected with each state being an electorate. This meant a high turnover of senators, giving more people a shorter role in public life, and it clearly defined them as reviewers. The role of the senate is murkier now: it entrenches the role of party in political life (through election and balance of power contests), senators have long political lives and it has become a place that otherwise unelectable powerbrokers go to sort out their superannuation (e.g. Graham Richardson, Noel Crichton-Browne).