All designs slow unloading to the compressed belt output speed if the supply is constant - it's the output belts, not the buffer chests, that are the ultimate limiters. Unbalanced buffer chest designs just get closer to that limit faster.
What's important to note is not so much whether or not the buffer chests are unloaded in a balanced way, but is there enough time for a train to be replaced with another (cycle time) without starving the compressed output belts.
This cycle time is where unbalanced buffer chest unloading shows its brittleness. If one chest empties before the next train arrives, it can starve the output lines even though the others still have lots of items built up. Essentially, unbalanced buffer chests can give you less time to cycle trains.
If you look at my (unbalanced) design in a production environment, there is barely enough time to cycle trains with nuclear fuel. But there is enough time. So, given a constant supply of trains the unbalanced chests aren't relevant.
If you can't get trains in fast enough for any design then it doesn't much matter what design you use to unload as all of their output belts will be starved by insufficient supply. What they look like when they're starved, in my opinion, is irrelevant. If they're starved in some manner (whatever manner), the problem is that you need more supply not that the unloader isn't working well.
If there's a more efficient 4-lane per wagon unloader than the one I posted above, I haven't seen it (and would love to).. but there's no denying that it's tough to meet its cycle time requirements. I do wonder if some of its brittleness can be corrected with lane preferences set in the splitters, but I haven't played in a while to test it. And some of the other designs with a similar footprint that are less brittle (more balanced) aren't really that much less efficient that they should be set aside.
To give you an idea of how I think stations should function to meet such tight cycle times, here's my solution to zOldBulldog's orphan train problem. I don't think I described it very well, but if you drop the blueprint into a creative mode game and have a look it's not that complicated.