HN routinely shadowbans and apparently shadow-pins with at least some frequency per this very thread. It's not an organisation that warrants assuming good faith.
HN's hellbans aren't real shadowbans, because other users can see them. They just have to opt-in to seeing potentially offensive content (it's a setting in your profile). Other users can even make banned users' posts visible to everyone!
Believe me, the people who are phased out deserve to be. I've had the unlucky experience of using an HN client that showed all comments by default, and you wouldn't believe the amount of deranged, vile shit that gets posted here.
