There are over 2.6M accounts on Hive, so which ones were excluded?

I don't think the comparison is fair. In real world rich people hold assets that appreciate in fiat value, they borrow against those assets to avoid taxation on gains and they benefit from inflation. Here accounts that are considered wealthy hold the asset that is direct subject of inflation and price fluctuations (historically a sharp drop). In other words it is not like 25 accounts control half of Hive, more like 25 accounts pay half of all the bills (not even counting the bills paid outside of Hive).