I think we're in violent agreement here, the case you note is exactly why key distribution matters. But even more than that the distribution of value lifetime m

I think we're in violent agreement here, the case you note is exactly why key distribution matters. But even more than that the distribution of value lifetime matters too, if a lot of the values stored are very short lived then not only do they not get rewritten many times but you also get to only ever write them as part of sequential batches (no random seeks). The compressibility of your data also makes a big difference, if intra-key compression is effective on your data that can easily be 1.5x to 3x reduction in the footprint on disk. So, benchmark your workload.