and everyone knows it
https://www.bloomberg.com/news/articles/2021-10-25/bitcoin-still-concentrated-in-few-hands-study-finds

"NBER researchers were able to find the former controlled about 5.5 million Bitcoin at the end of last year while the latter controlled about 8.5 million. Additionally, the top 1,000 individual investors controlled about 3 million, and the concentration could be even greater."

“This measurement of concentration most likely is an understatement since we cannot rule out that some of the largest addresses are controlled by the same entity,” researchers Igor Makarov and Antoinette Schoar wrote.

For instance, the data did not not assign the ownership of early Bitcoins held in about 20,000 addresses to one person (Satoshi Nakamoto) and considered them as belonging to 20,000 different individuals.

The concentration of miners is even more profound, data show. NBER found that the top 10% of miners control 90% of the Bitcoin mining capacity, and just 0.1% (about 50 miners) control 50% of mining capacity.

Such a high concentration could make the Bitcoin network vulnerable to a 51% attack, where a colluding set of miners or one miner is able to take control of a majority of the network. NBER found the concentration also decreases following sharp increases in the Bitcoin price, meaning the probability the network is vulnerable to a 51% attack is higher when Bitcoin’s price drops sharply.

www.engadgethd.com - the other stuff i'm looking at