Looks that way to me... I really liked a LOT about MongoDB, I don't think they had a good story for administration of scale + redundancy. RethinkDB, Cassandra and others have a ring + redundancy model which I think is easier to deal with. Where Mongo at least was limited to replication or sharding, and was a serious pain to deal with from the admin side imo.

Understanding the advantages and shortfalls is sometimes harder too. Mongo having multiple secondary indexes is pretty nice as well. Haven't dug into FerretDB, my first question is if it will run over the top of CockroachDB, as that's how I would probably want it configured. Then, I'm not sure if I wouldn't just use the JSONB surface in PostgreSQL/CockroachDB directly.

I think it just really depends on how/what you need to accomplish.