With the exception of private groups (when they've been properly developed), feeds don't really replace those.  

 I don't know what feeds are. But Dan mostly wanted to know what posts don't get deleted. So it's another key difference between tags and communities 

 Feeds are a newish thing, maybe only coracle uses them atm. They work the same as bluesky feeds, basically different filters eg filtering to only show posts about Gardening would be a Gardening Feed:)

I'm not sure about post deletions 🤔 

 All apps will end up as half assed browsers. Wasted effort.