This made me realise something, on Mastodon we can hide our subscribers and subscriptions, but if the people we subscribe to and who subscribe to us don't do the same, it's useless... I mean, yes it makes it harder to get that information, but it doesn't make it impossible to get.
I tried with a small account, on a small server, these subscribers and subscriptions are hidden. All I had to do was scan all the accounts on this server to find 63% of its subscriptions.