Piefed has some great features for discoverability, like feeds, but afaik every fedi reddit clone still suffers from the problem that someone from your instance has to subscribe to a remote community before it shows up at all. So if everyone just picks an instance and sticks with it, the federation never happens. It also promotes a more centralized fediverse because more populated instances will both be more likely to have a local community for a topic and to have at least one user subscribe to any given remote community.

As an individual, it's difficult/impossible to keep up with everything or to discover new things because there is no true r/all equivalent. You'd need to browse multile instances or use external tools regularly to check on fediverse activity.