Gary Gensler doesn't understand that the decentralization of bitcoin is about the full nodes and the miners involved, not about the number of wallets containing big funds (and frankly, those are still plenty too).
And allow me to be a bit mean: maybe he confused it with Ethereum.
The network may be "decentralized"...but what happens when big companies, governments, and institutions accumulate all of the BTC (or at least, most of it)? Without people "owning" BTC (self custody), the blockchain will become the sole playground of the aforementioned entities. I could be wrong, though.