> Cryptocurrencies have long made promises of decentralisation and fairness and, despite that, people still centralise around exchanges in the same way that people centralise around traditional banks.

This is the value of crypto. People can choose how much they want to trust 3rd parties and how much personal responsibility they want to take on. Some people may always choose a centralized mechanism for managing their assets, some will choose to manage their assets completely on their own, and others will decide on a case-by-case basis if they want a 3rd party involved.