One part of this (which isn't really covered in the article) is that Google historically had a give-and-take relationship with people gaming search engine results. SEO has been a thing for a long time, and it's impossible to make it go away. However, Google used to punish sites that took it too far. It wasn't necessarily ideal, but it worked well enough to keep egregious spam out of the top level results, and companies could still direct users to their site when they had something they were actually looking for. SEO consulting companies sprang up who knew Google's rules well, and that arguably meant a bunch of grifters being overpaid, but at least the results stayed relevant.
Google seems to have given up on enforcing many of those rules.
I think you could do it in Lemmy itself combined with RSS feeds. The mods would curate a list of RSS feeds, and use the keywords to pick the ones for a bot to automatically post (which means if a programming blog did a post about windsurfing, it wouldn't show up as long as the meta keywords didn't match). Mods could take suggestions each week for feeds to add or remove.