Know Your Customer requirement doesn't ruin the decentralization of Bitcoin, nor does the AML policy. What destroys Bitcoin decentralization is the fact that centralized companies, i.e. companies like Binance, Coinbase, BlackRock, Fidelity and others destroy the decentralization. The fact that Trump (if he wins) plans to make the rest of the Bitcoins labeled as Made In The USA, kills the decentralization.
When centralized companies, that are managed and regulated by a certain group of people or by the governments, take their hands on a majority of coins, miners, nodes and so on, that process is what kills decentralization.
From a purely network decentralisation point of view, the KYC requirements indeed don't matter (unless they could get expanded on miners etc), but apart from network decentralisation, there's another crucial feature of Bitcoin - censorship resistance.
If we sleep-walk into a reality where all Bitcoin transactions are only done by verified users using KYC-compliant exchanges/wallets with any peer-to-peer platforms or non-custodial wallets delegalised, that feature could get heavily crippled.
And I don't think Blackrock or alike would care too much about taking control over Bitcoin's network. It wouldn't make much sense for them to attempt that, unless we're talking about some larger plot involving governments and three-letter agencies.