I am more worried about some dedicated reddit, or 4chan user getting angry than the feds. I'm weird with this because when I write posts I wait 2 minutes, and think how would feds interpret my posts, and is it worth posting that.
I will most likely make a mistake with my anonymity one day, but to have alts increase anonymity wouldn't you have to be good at changing your writing style?
My understanding is this kind of opsec is basically entirely to avoid random 4chan/kiwifarm psychos. You're right that the feds can 100 percent find out who you are easily if they want to if they don't already know. Don't have a firm opinion on how likely it is for the former group to actually try to fuck with you though, (blessedly) don't have direct experience there.