the numbers are not an easy task, you can't get an accurate number unless you have a massive server centralized and you are counting non stop, which is not efficient and against the ethos of decentralization. Amethyst for new accounts and small follow does a decent job, but once your follow increase and if your account is aging is more challenging

I believe that among the clients the most centralized is Primal (I personally stay away from it, censoring relays and seems to be very accurate at counting follows even for old accounts), no good opsec , that is already a no no for anyone that is here for the Nostr ethos