> Syncing that local CouchDB to your web based CouchDB is very fast

This is not true. When you compare the CouchDB replication with other replication protocols, it is slow. The reason is that CouchDB supports replication with many instances at the same time. This creates big overhead in handling revision trees. Many requests have to be made all the time. You can observe that by starting the PouchDB subproject in the comparison repo. Watch the network tab in dev tools. Another problem is that CouchDB does not support Websocket replication, everything is long polling and plain http requests.

Other replications that only support many-clients-to-one-server are way faster. Both, on the initial load and on ongoing changes. This was the main reason why I build GraphQL replication for RxDB.