Misskey, Calckey, Pleroma, Mastodon- All perform the same essential function. Microblogging (with minor differences e.g Pleroma has a 5000 word limit per post) Think Twitter.

Pixelfed is an image sharing platform - Think Instagram.

Friendica will give you a similar experience to Facebook (Macroblogging)

None of those platforms have real messaging (Direct messages, but not private or encrypted)

Almost all sites have an RSS feed...

https://rss.com/blog/ as some advice on finding them...

Even a lot of fediverse platforms e.g Mastodon have RSS 👍

XMPP rooms a generally limited... but you can use the bridging function to access Matrix rooms, which there are more of ATM

https://github.com/matrix-org/matrix-bifrost/wiki/Address-syntax

Better marketing? Not sure...

And given #xmpp can do things like !movim @lemmy.ml, it's a shame it's not me widely used.

Using lemmy directly will give you more control over the post and lemmy specific features...