Bitcoin is everything, store of value, payment option and a step away from banks but with the way are looking now I don't believe in bitcoin been decentralised anymore, no one told me that centralised entities will be buying bitcoin massively so that they can start controlling Bitcoin.
If the entities can control Bitcoin how is it still decentralised? Anyways, you are free to use Bitcoin for anything but I believe Bitcoin isn't perfectly made, and it's possible that nothing will be ever created to better Bitcoin.
I don't think the institutions and whales cannot buy all the bitcoin. Also, the bitcoin supply is limited and short, therefore it is not possible for anyone to buy bitcoin at low prices. If you start to buy bitcoin from the open market (and not through the OTC deals), the orderbooks would be quite thin keeping in view of the demand of bitcoin.
As far as the debate about whether Bitcoin is centralized or decentralized, then in its true essence, Bitcoin is decentralized, but it has a public ledger, and all the transactions are publicly available and can be traced. Keeping Bitcoin on CEX means you're just not utilizing any decentralized feature.