Oh that's really neat, thanks for sharing!!:-)
From other comments here, I am piecing together the fact that - probably since instance blocks don't truly exist in Lemmy - the Lemmy side implements these blocks as "community" ones, while the PieFed side either does the same and I simply did not comprehend the difference at the time or else it might use PieFed's instance blocking functionality. Someone on the PieFed side could test this by looking at this OP to see if comments from people on a blocked-by-default instance (Hexbear.net?) are visible, since those would be hidden by an instance block but not a community one.
Either way, having such optional functionality even further strengthens my respect of the .zip pair of instances - those admins seem really on the ball, working hard to truly care for the people who join:-). Lemmy vs. PieFed software seems far less relevant than having such a great admin team vs. not.
Fwiw Lemmy.World has >6-fold more users on it than the 2nd-largest Lemmy instance. https://lemmy.fediverse.observer/list
The Fediverse is shrinking https://lemmy.fediverse.observer/stats&months=48.
And people cite how it is our toxicity that pushes them away. https://www.reddit.com/r/fossdroid/comments/1uiywal/should_we_switch_to_lemmy/.
Many trolls exist on Lemmy.World but also sth like >90% of the most active communities are there too. People can help spread this around by posting, commenting, and voting in communities based elsewhere across the Threadiverse.
Though OP is correct also that in threads such as this one, oftentimes the most acutely aggressive and adversarial responses come from Hexbear (although not possible in this case since the community is located on an instance that has defederated from it) or from Lemmy.ml - the numeric number of trolls is not necessarily higher but the relative level of enrichment is.