A few thoughts going in: I think attaching representation to land or anything static will backfire long-term since there's no guarantee that the groups given disproportionate representation in a hundred years will actually deserve it. I think it's also better to have a strong executive as long as they aren't too extreme. Also, all things being equal, I think it's better to have six moderates in a row rather than alternate between far left and far right candidates.
My current proposal is this: Have a proportionally elected Parliament with 1,000 members and no minimum threshold for party entry. Use ranked choice voting within Parliament to select an executive, which assures they will represent the median voter. Then allow laws to pass with 40% of the legislature plus the executive. At any time, Parliament can hold a vote of no confidence with a simple majority, triggering another RCV for an executive.
I think RCV and no confidence options will be a check against dictatorship, and the 40% threshold will mean tiny extremist parties aren't able to hold a moderate agenda hostage. Eliminating the threshold for entry will also mean large parties split when they get too big, and heck, the max size of a party could even be capped at 100 seats or something. In theory you could have two parties that act as one, but with enough friction between them, it will be too politically tempting for them to compete with each other.
The main benefit here will be getting a lot of moderate reforms through fast, and also that voters don't overcompensate for bad governance by turning to extremists. As long as the moderate executive is getting things done, I think votes of no confidence would be used sparingly (and even if they were frequent, the instant RCV would save a lot of time without requiring a ton of time for coalition building). This requires Parliament to select a consistent vision (represented by the executive), but it will be one that represents the median voter.