The biggest ether-holder right now the Ethereum network itself, and the smart contracts on the blockchain. Usually exchanges have the biggest bag of coins, tokens, and when users start to withdraw them, its commonly interpret as sign of incoming bullrun. Because you withdraw it, if you dont want to sell, but waiting for higher prices.
Ether can be deposited into smart contracts, dapps, and liquidity pools, for nice yields, and holders like this. So currently the exchanges became the minor holders, with 15,5 million of ether, compared to the 18 million ether on the Ethereum network.