That doesn’t mean centralization. It doesn’t matter who owns how much Bitcoin.
Convince me that the coins purchased by BlackRock for their bitcoin ETFs are not centralized to them and the people who invest with them are not subject to any actions and decisions they take? Moreover, their profitability potential is lower since BlackRock would share their profits with them and if anything happens to BlackRock and they stop functioning tomorrow, would the investors have any claim to their coins?
Bitcoin isn’t proof-of-stake where those with the most coins make the decisions. Bitcoin is a peer-to-peer monetary network. As long as you can run your own node, and running a node remains cheap and accessible to everyone, and as long as you can choose which software to use, you don’t need to worry about centralization.
Are you still on topic? how can they run their own nodes when they are not directly in possession of the coins, but are offered shares that reflect the spot price of bitcoin at the time of purchase? You can only run a node for more privacy when you've the UTXO to spend. The coins are held by the ETF's companies and are managed and traded on behalf of the investor. Investors choose this channel when they want exposure to bitcoin, but do not want to manage it by themselves.