The trouble with coupling the two is that now I have to either trust some third party db service, or some custom db. The DB is so fundamental, and so hard to g

The trouble with coupling the two is that now I have to either trust some third party db service, or some custom db. The DB is so fundamental, and so hard to get right / scale, that it's hard to trust a startup to do it well. We use Firebase and even with all the resources google has this has a lot of issues (especially with the client libs).