I believe OP has got a point and while I agree with the majority that bitcoin remains decentralised in reality, the increasing adoption by institutions, buying on centralised exchanges, use as an investment and not P2P, etc., at least make it more centralised than it was intended to be.
No, Bitcoin is still decentralized. It is an internal property of Bitcoin. The only thing big groups can do is manipulate the price by buying/selling.
This is probably what @mrquackquack meant when he spoke about the decentralization of bitcoin (although this is not entirely correct), when large holders of bitcoin can influence the price and manipulate the market.
This is where I think he has a point but not only in that, but a truly decentralised use would be P2P, and today such use is minimal.