I have checked the richlist recently, some of them are from exchanges. More than 50% of BTC are holding by the top 50 people or so. Can't remember the amount though.
I have two question-
1. Exchanges are being the giant although BTC holding by them are from customers. Still it's possible that they are trying to be a controller of the crypto community which is very bad I guess.
That's the sole reason why they say that you should never keep a large amount in exchanges. You must only keep a certain amount in exchanges which you want to actively trade and are willing to lose. The rest of your coins should be in a wallet whose private key you own.
2. If top 50 people hold 50% of BTC and BTC becomes the global currency, we may face once again the previous era. Being slaver to certain people.
Think at from the point of macro economy. In my opinion, it's something we need to talk.
This issue does exist today but will vanish in time when many people join the crypto community and the amount of bitcoin gets distributed in the community.