It's a fair point. I mean, how can Bitcoin become Fiat's successor if it isn't recognized as legal tender? At least, one country (El Salvador) decided to "break the ice". It'll be up to other countries (especially developed ones) to do the same in order to help make "hyperbitcoinization" a reality.
I think it's very unlikely Bitcoin will become the "Global Unit of Account" simply because Fiat is still a dominant force in our economy. Banks are relevant these days even with crypto/blockchain tech in play. They will eventually adapt themselves to the latest trends in the Fintech space, as they phase out paper money for good (in exchange for CBDCs). Bitcoin will only remain as an alternative to the existing banking system because of its decentralized and censorship-resistant design. I'm fine with that as long as people are able to obtain financial freedom. Just my thoughts