the Sub is supposed to be the one that’s actually in control
This is a myth, presumably meant to be reassuring to subs that are new to BDSM, at the expense of risk awareness. In principle the sub is no more “in control” than the dom is, and in practice they are often significantly less so.
ActivityPub votes are public by design, Lemmy just hides the voters from users, while Mbin displays them. Anyone can also spin up their own instance and get access to the data.
PieFed recently added a feature to pseudonymize votes. When enabled, your votes are labeled with the name of a shadow account linked to yours, but only the administrators of your instance know that it belongs to you.