This is incorrect. You don’t have to host your own tangled appvew to log into tangled without having your atproto account on Bluesky’s PDSes.

You CAN host your own Tangled AppView. You CAN host your own knot. You DO NOT have to in order to self host your own PDS. Each of these layers are decentralized from the other.

Nit pick: the layers are decoupled from each other, not decentralized. The data layer is internally decentralized. AppViews are a layer of centralized projections of the decentralized data layer.