I'm not sure which components are redundant here, but my guess would be the AppView because:

"An App View is the piece that actually assembles your feed and all the other data you see in the app"

So it seems that if the App View is down, you don't see your feed.

Of course, if your PDS is down you won't get any new messages either.

If a PDS can subscribe to multiple App Views, and it will catch up after it has been down (as opposed to just missing those messages/events), then that doesn't seem too bad.

Feed generators and labelers appear to be optional, though not much is said about them.