For some reason, a lot of these search engines like to brag about the number of documents in their index, which never made sense to me. Maybe it was true in the past, but on the modern web, larger index !== better results. In fact, I'd argue the opposite since you're much more likely to serve SEO spam.
That was my motivation to start hacking around on CrowdView (https://crew-rho.vercel.app), a search engine specifically for forums and discussion content (e.g. forums, discords, twitter, reddit, etc). It has a curated index (today, curated by yours truly) to remove SEO junk and help you figure out "what does a real, genuine human think about this think?"