Back in the old days, activitypub was my Rss feed reader. Discoverability was driven by good old fashioned cross linking, comment discussions, and skimmable feeds from aggregators like the one we're on.

People love to reinvent the wheel and claim it's a whole new thing. No ideas on the web have really been innovative since the bubble popped. The innovation has all been on delivery and execution (not wanting to discount any of that).