I'm still reading through the article, but can you give an example of why rendering all the blocks ordered[0] by (min x, min y, min z) lexicographically doesn't work[1]? I thought the sophistications is necessary for performance only, i.e. not drawing anything that doesn't appear in the final result.

[0] Assuming (0, 0, 0) it's in the middle at the top of the screen.

[1] Assuming this is what you meant by "simple back-to-front".