Hello! I saw your Cohost post and was wondering if you know what their moderation and Trust & Safety team is like. I have seen a lot of people harass folks to no end on tumblr, for no apparent reason even with innocuous fics, with unfortunately no action on the tumblr staffs' part, and frankly I am terrified it will eventually happen to me. This would be the main reason, alongside the algorithm stuff, that I would move to it.
honestly like. your mileage is going to vary depending on any site. cohost has a fairly clearly-written Community Guidelines page that outlines most of the behavior that can and will be enforced to prevent harassment and abuse, and since the company that runs ASSC is much more worker-focused (e.g. not advertiser-focused) i personally have a much greater degree of trust in them than i do in twitter or tumblr. But look, like, that's just my opinion. Obviously, only time will tell how they react to things like that, but my guess based on the staff's behavior so far is that "i think they'll handle it in a good way".
FWIW the lack of algorithm also contributes positively to this, imo -- no "random posts" in your feeds means you have less exposure to users/posts that you have not personally opted in to see. that in itself GENERALLY dampens the effect of harassment campaigns.
that said, there's also a pretty hefty set of tools that you, the individual user, can use to protect yourself -- going private on a blog means ALL YOUR CONTENT (comments, posts, reblogs, everything) is hidden from non-followers. none of this "well if you left a comment on a post a while back it'll still show up" shit that happens on tumblr. so that's a good Nuclear Lockdown if you need it.