I did something similar 2 days ago with ViolentMonkey if you only want to check high-level discussion without any new tabs at all.

https://greasyfork.s3.us-east-2.amazonaws.com/sokzpb2ztmatlh... (screenshot)

https://greasyfork.org/en/scripts/588721-hacker-news-comment...

I'd improve it by counting top level comments next to items but that would slow it down. Still need to make some slight changes like closing sidebar by re-clicking orange (beyond just right-clicking sidebar.)

It's very fast and speeds up thinking overall.