Interesting that everyone here wants to operate their feed on a blacklist basis. Personally I'd love the opposite, to be able to subscribe to instances or specific communities and only get content from those. The main reason I used Reddit over anything else is because it only showed you posts from subs you subscribed to.
Weird, it doesn't work for me for some reason, I have to manually go into the "subscribed" tab each time. Also my point about not being able to subscribe to entire instances still stands. For instance(heh) bookwormstory.social is an instance dedicated to discussing a specific book series and currently has like 5 communities, and I'd have no way of knowing when they started a new community unless I manually checked.
Hopefully you'll get things sorted with getting subscribed as default view.
I agree that it would be useful to be able to subscribe to a whole instance, but I think there are quite some technical hurdles to get there.