I disagree with this assertion. Shadow-banning on HN is quite well known, and any troll worthy of the term understands the landscape of their endeavors.
>banned regularly so it effectively doubles their work
How is opening a link once a day or so in incognito mode to check for their comment effectively doubling their work?
>Quite often their willingness to invest time into trolling drops off with lack of response so often they will leave before they understand that shadow banning is a thing.
Again, I think we both have very different ideas on the transience of a trolling campaign. I assure you, once someone is determined to troll a specific community, its a much longer commitment than you are estimating.
Edit: Impressive. Down-voted for stating my disagreements with counter-points.
If the downvote was unfair, someone often comes along and fixes it; and if it was fair, then you should reflect on what you said. Either way, the impulse to complain should be held in check.
From my personal experience having dealt with trolls on other popular forums and implementing shadow bans myself previously my experience runs counter to your beliefs.
You don't have to catch every troll with shadow bans. You make the experience for the new ones unenjoyable by removing their feedback and they are more likely to move on before they become committed enough to start cycling accounts.
If someone is determined to troll a community than no form of protection other than brute force moderation will work but compared to the number of trolls out there the number that rise to that level of abuse are very small.