Again, you said there are an infinite number of proportional systems that we could have. There are two winner-take-all systems that I think are being seriously considered: alternative vote and first past the post. There's not much that you can do other than change the borders.
One point I will make on party power is that we often talk about it as if it is a horrible thing. When I think of party power, in the best-case scenario, it is members getting together and making decisions. That's something that you try to control in any system, and if we adopt an open-list PR system and focus on democratizing political parties, I don't think that would be a bad thing.