There's also something to be said about how Google should be returning information, not answers. Skip to the 1:00 mark in this Technology Connections video where he demonstrates how if you ask Google when the touch lamp was invented it'll pop up with a giant, confident answer of 1984, despite the fact that if you do the research yourself you can find the first patent for it was filed in 1954.
As far as the thought experiment goes for making up rules, you could probably have a threshold where advertising ability gets cut off and it would do enough.
It's certainly controversial so all I can give you is a subjective viewpoint but yes, objectively these things make search engines more convenient but cut the traffic to the original websites by a small margin.
So far, I've noticed Brave Search only shows sidebar results for Stackoverflow and a few other popular forums that do not advertise on their pages directly, nothing else. So they're not really taking any revenue away. As for npmjs thing, I'm not sure if their revenue is hurt in any way because to view the package documentation you still need to open the link. Brave Search just provides you a copy command button extra for convenience.
As for discussions, they do not give full context so you always need to click the link so that's great for website owners as they get more exposure and traffic too.
At this point, Brave Search features are more on the UX side of things than anti-competitive so I personally will hold off the tinfoil hat for now.