I question "<<" at this point. Maybe "<", but the gap isn't as large as you expect.
It's not going to be as impactful as r/all being removed, but removing google searchability would probaly do more harm to traffic than it does benefit to the site.
>here's a reason Facebook blocks Google indexing (for the most part), and it's because Facebook wants people to be using Facebook, not Google.
I think it's more because Facebook is an inherently more private site. It has public groups but Facebook wasn't made (by default) to have every post you make be searchable from Google.
You search on Facebook for people, and you care about who they are. You search for content on reddit and don't care who redditors are.
For Facebook, it was only private in the sense that the greater general public couldn't see your content, but that's really just unrelated third parties and Google. The stuff you post on Facebook was effectively public in the people around you could all see it.
I've used the old.reddit site and ads don't really bother me. On the other hand I've often found the solution to a problem on Google pointing to a Reddit post.