Agreed that people who need strong privacy should use something like Signal (or maybe Matrix or XMPP). And also agreed that RSS feeds are a privacy hole on most of the fediverse; Hometown and GoToSocial both disable them by default, Mastodon should do the same.
Nothing prevents malicious actors who want to make enough of an effort from creating accounts on instances (or for that matter Matrix chat rooms). But that's not feasible for broad data harvesting by Meta.