Thanks for the links. I see your point. It's a bit like when you compare the wealth between Germany or Japan with the one of the Chad or Malawi. But while in GER and JP the average person had already 20 years to aggregate wealth, in the latter two countries more than half the population is not even grown up.
My calculation only includes the top 1,000 (top 100-1,100) users of which most are very active on steemit since at least half a year. You can see that in the fact that the lowest account value is slightly more than 10,000$. Therefore I think the time question can be ignored in this case.