Some members said that they wouldn't change a thing from this crypto-sphere we live in, but IMO there are a lot of things that should be changed and a huge room to improve.
If I had to choose one, maybe the market dominance of Binance would be the one that I would choose as per today. It is dangerous when a monopoly like that dominates in such a degree a certain market, and in my understanding of the underlying values in the creation of Bitcoin, I think that it goes against Satoshi's vision.
Even if you can change one CEX to be dominant on the market, this does not mean that another one will not appear, because if you remove one, someone else will take advantage of that opportunity. In addition, you should take into account that Bitcoin was created for everyone, and that Satoshi did not in his vision go with any restrictions in terms of how mining or trading will be done.
It might have been better if we had DEX from the beginning, but no one could in any way prevent people from starting a business with CEX, which turned out to be extremely profitable for the owners, and on the other hand, a simple way for users to buy and sell Bitcoin. What is wrong in that whole story is that CEX started to present themselves as some kind of crypto bank, and many users started to use them in that way.
If there was a law that CEX could not keep the user's coins for more than 48 hours after the purchase, then clients would be forced to keep their coins in non-custodial wallets and this would somewhat prevent the centralization of millions of BTC in custody services.
Of course, something like that will not happen, because if we know that CZ indirectly called its users stupid in the sense that they are not able to store their coins independently, it is more than clear that they want you to buy something, and then leave it for them to keep.