It doesn’t quite all show up the feed no matter what instance someone is on. In order for content to federate on an instance someone on that instance has to directly access it. I think this is why small niche instances appear to have a trickle of content on “all”.

Same. I’ve been very surprised to see so few mention this problem and I threads where it’s brought up it’s dismissed as a temporary issue or even a feature. It’s been like this for a month on lemmy.world and many other instances. For me it makes it nearly unusable and I usually go to kbin instead.