It's nice to see the analysis, and "who's who." This does hint at the beginning of decentralization, at least.

What would be an even deeper indication of decentralization would be to look at what it takes to be in — let's say — 200th place on the richlist, and then the week-over-week growth rate of what it takes to maintain 200th place... that would hint not only at the depth of decentralization, but at the direction of stakeholding trends... is POB becoming more decentralized (more scattered staking) or less decentralized (staking more focused among the primary holders).

But thanks for doing this; I do have a fondness for statistics!