What do you mean by decentralised coin in your last paragraph? A coin is a coin everywhere no matter the exchange it is traded, whether centralised or decentralised it does not matter. All of them also get manipulated by whales. Crypto manipulation is worse than forex manipulation because in crypto a single person with large quantity of a coin can influence price by dumping it but that is not how it works in forex trading. You will need a big institution to be able to move the market with their orders in forex trading.
Centralized is very important figure because it shows the ownership of the coin. Like for example with Bitcoin there is nobody that can control it, which means that it's decentralized and that's the most important part of the deal and could be done a lot better.
Whereas the coins like BNB and XRP for example have centralized ownership, BNB is owned by Binance, while we can own the coin itself, the ruler of it and controller of it is Binance team which means that they can print whatever they want and whenever they want, or XRP could be very important and Ripple is the most important stuff and that makes it most important part. This is why I believe we should consider how this could be important and could change a lot of stuff on the long future as well.