You're basically saying: don't use mongo. It's trivial to emulate a blob of data in a relational database; just use a... blob of data. Or any of the many, many other options at you fingertips. Conversely, manually implementing efficient joins is a total hassle and it'll probably end up slow and brittle. At the very least you'll need indexes and that means an (implied) schema.

So in the normal mongo usecase for storing (as opposed to caching) data with relations, let me see if I can summarize:

- you can have relations, it's just mongo won't help you deal with then: you just need to implement them yourself.

- you can have (actually need) a schema, it's just mongo won't help you deal with that; you'll need to implement that yourself. Have lots of fun with schema-changes, especially because...

- Since you're changing decoupled entities, you need to keep them in sync. You can (and probably should) use transactions, but mongo won't help you with that. You also probably want foreign keys, but mongo won't help you with that either. Migrations on mongo are a special kind of terrifying.

But hey, on the upside, it can store structured blobs, and it's probably hardly any slower that your filesystem, which could do that too.