Well, one site allows anonymous posting and practices open banning, while the other practices hellbanning and has the "karma" system which weights a users' posts as a function of their alignment with the norms of the community. They have completely different approaches to curating user identity and controlling conversation which I think are mutually exclusive, though both appear to be effective in their own way.
It would be interesting to see a post or an article comparing and contrasting the different methodologies between the two sites.
Which is why I worry about the government moves we are seeing against online anonymity (looks to me like the ground is slowly being prepared to make it illegal).
I don't think the HN way is effective at all. Virtually every hellbanned user I've ever seen doesn't appear to have done anything wrong. So they keep posting, having no idea they broke any rules, until they realize they were banned. Then they make a new account and continue on, not changing their behavior in any way, as they have no idea what caused the ban in the first place.
Shadow bans were created originally to deal with trolls. People deliberately posting garbage. It is counter productive to use shadow bans on contributing people who happened to break an unspoken rule like "don't criticize pg".
So they keep posting, having no idea they broke any rules, until they realize they were banned. Then they make a new account and continue on, not changing their behavior in any way, as they have no idea what caused the ban in the first place.
The problem with it is it makes one particular set of assumptions about behavior - you must be a troll, you must crave attention, and in the absence of attention, you must either get frustrated and leave or else continue trolling. Because being a troll with no possible valid input to offer or being a good user is a binary state.
But of course if you look at the comments by most of those users, you'll see a number of perfectly reasonable banned comments and maybe (if you can find it) the one infraction which may have started it all. For most of them, I wind up wondering if a simple warning from a mod might have sufficed.
And yes, as you point out, legitimate posters who just lost their head for a moment go on talking to an empty room while the actual trolls just burn another account.
Shadowbans are abused all the time in Reddit, for example. Not the sitewide sbans, but the ones done using AutoModerator, where they delete your comment with no warning, and you don't find out because you still see your own comments.
/r/Games for instance, has a policy of arbitrary banning people this way.
It would be interesting to see a post or an article comparing and contrasting the different methodologies between the two sites.