Best estimates are that there are about one million 
  holders of Bitcoin;  47 individuals hold about 30 percent, 
  another 900 hold a further 20 percent, the next 10,000 
  about 25% and another million about 20%, with 5% being 
  lost.  So 1/10th of one percent represent about half the 
  holdings of Bitcoin and 1 percent close to 80 percent 
  (http://www.businessinsider.com/927-people-own-half-
  of-the-bitcoins-2013-12). The concentration of Litecoin 
  ownership is similar 
  (http://litecoin-rich-list.blogspot.com).  
  Most of the big wallets have been in place from early on, 
  so sitting back and watching your capital grow has been a 
  very successful strategy.


  The distribution of Bitcoin holdings  looks much like the 
  distribution of wealth in North Korea and makes the 
  China’s and even the US’ wealth distribution look like 
  that of a workers’ paradise [1]


  Both Bitcoin and Ethereum mining are very centralized, 
  with the top four miners in Bitcoin and the top three 
  miners in Ethereum controlling more than 50% of the hash rate. [2]

Even taking a conservative skewed estimate [3] of wealth distribution in Bitcoin, it's about twice as worse than normal capital oligarchy. This is because PoW* style cryptocoins allow anyone with capital to proportionally extract the limited supply of Bitcoins/Cryptocoins/Altcoins/Tokens/Etc - but often significantly worse due to how Satoshi style PoW algorithms produce the majority of the supply in a short time frame. Worse yet are the premined networks, like Ripple, NEM, ERC20 Tokens, NEO, Ethereum, and so on.

[1] http://www.businessinsider.com/bitcoin-inequality-2014-1

[2] http://hackingdistributed.com/2018/01/15/decentralization-bi...

[3] https://medium.com/@BambouClub/are-you-in-the-bitcoin-1-a-ne...

* Proof of Stake will exacerbate wealth centralization, due to statistical probability of block rewards going to the wealthiest, perpetually increasing their odds of further newly minted coins.