As someone who argues routinely with long-winded racists on Reddit, it's no haven. Nor are the crackpots spewing 1/6 rants and COVID conspiracies on Facebook.
I think social media itself is the problem, not the post length.
Platform features and limitations do matter. Tumblr is considered the original rage mob platform, because the only way to write an extended response to a post was via reblog, so if you ranted about something you hate, you'd put that something in front of your followers to hate too. Good engagement though, so now that feature is everywhere.