I'm afraid he's right, especially when CEXs hold most of BTC's circulating supply (eg: Binance). It's even worse now with the recent approval of spot Bitcoin ETFs by the SEC. Institutional investment companies like BlackRock, VanEck, and MicroStrategy are accumulating large amounts of the cryptocurrency.
Yes, I think this is a problem (not a very severe one however, see below). However, the answer to the question if Bitcoin is "less decentralized" due to developments like the ETF approvals in the US for me has no easy answer.
I disagree somewhat with this popular meaning for example:
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).
My assessment is that both are important: the "mining decentralization" and the "economic decentralization". The "users" (also called "economic nodes") have the power to accept or not accept the blocks the miners mine, so if a miner cartel tried to mine with an updated code changing important parameters (e.g. the 21 million limit) the economic nodes can accept them or not. The more concentrated these nodes are, the more likely it is that they could also be co-opted by the miners cartel. And let me not even begin mentioning gubermental pressure, above all if services are too concentrated in one region like the US.
@adaseb has a point when he writes that the CEX's/ETF's funds are not their property but their customers'. That is correct. However, this does not mean these entities don't play a role in the power structure of the Bitcoin ecosystem.
One example is for example what happened in 2017 when the big block/small block war was fought out. We were lucky that almost all exchanges preserved the "Bitcoin" moniker for the original chain, and not for the hard forked chain today called "B[itcoin] Cash". Such an event can repeat. The problem is that while in theory customers could boycott/leave an exchange or ETF "behaving maliciously", most customers are quite passive and would simply accept what the exchange or service provider is doing.
So in general it does make sense to educate people that they should try to hold their Bitcoins on their own wallets with their own keys. It would be better for the ecosystem in general. However, due to the multiplicity of economic actors, I currently don't see a critical situation. The US ETFs could even have improved the situation, as before the biggest exchanges (like Binance) were probably even more dominant.
If BTC becomes compromised, what's stopping us from moving to a more decentralized chain in the future (Litecoin, Monero)?
I think at least it's a good idea to have some strong decentralized "backup chains" just for the case. It would be healthy if there was a decentralized chain at least as strong as BNB for example, if not as Ethereum. But there seems a long way to go for that to happen, as presently 90%+ of the altcoin crowd doesn't care at all about decentralization. I'm optimistic for the long term though, eventually the centralized altcoin bubble will pop in my opinion.