There are an absolute shit-ton of features that PieFed has that Lemmy lacks. To give just one example, PieFed offers “polls”, which do not show up on Lemmy since the latter lacks the ability to properly receive them.

Even for the posts that do federate, many features cannot federate in Lemmy, since the latter lacks the entire concept of them - e.g. hashtags, user & post flairs, user labels, limitation of community voting to only subscribers, etc. To give an example there, if a Lemmy community wanted to see fewer posts about USA politics, a moderator only has one option: make a rule and ban users who try it. In contrast a PieFed community could make a community flair and have a much gentler rule that any post about USA politics must use that flair, so that users who did not want to see such could filter them out. PieFed also combines communities into cross-community topic areas, and combines all comments across all cross-posts (identical posts sent to different communities), with the ruleset of the one currently clicked on displayed at the bottom below a post, including the description and the entire set of rules that the mods are asking the members to follow (displayed on each and every single post). Therefore even the identical communities look different when on PieFed, with many enhanced features (caveat: 3rd party apps have not yet adapted to take advantage of most of these features).

https://join-lemmy.org/instances will send you to places like hexbear.net and lemmy.ml, whereas https://piefed.social/auth/instance_chooser literally never will.

Even federation works differently, allowing a hierarchy of level of “trustedness” beyond simply yes federate fully vs. no defederate entirely. Also PieFed instances more efficiently send out 25x less data per post, and new instances are significantly easier to install and maintain (see e.g. irl stories of https://jeena.net/lemmy-switch-to-piefed and https://slrpnk.net/post/29381524, and don’t miss how in both stories there are long-standing issues/bugs that somehow never seem to get fixed…). Feel free to like or dislike whatever you choose but…

Different federation, different posts, slightly different users. Different software means everything is now up to be changed, especially as the software is written in a language that encourages more contributors, and the devs are also much more responsive to feedback.

If you dont like it, fork it. Stop bothering us about it

- source: Nutomic, one of the primary Lemmy devs

Even the very model of interaction on PieFed profoundly differs from Lemmy: e.g. if I wanted to block political posts then I could unsubscribe from all (or most) of them, so that they do not pollute my Subscribed feed on the main page, yet they would all still then be just a click away in the News & Politics Topic Feed, meaning that I can literally both have my cake (no politics) and eat it too (have politics whenever I want). Everything is different here. Check it out if you do not believe me - e.g. your very own instance has a PieFed version.