Unrelated apps (https://leaflet.pub/, https://tangled.org/, http://semble.so/) don't go through Bluesky Appview (since they need aggregations of different kind of data). I think aggregation is the only model that can compete with centralized services on UX, but of course different apps would need different backends.

You may be confusing the Relay, a protocol component run by Bluesky, with the Bluesky AppView

https://atproto.com/articles/atproto-for-distsys-engineers