RDBM is optimized for file size; it is very much an artifact of its time, when hard drive space was limited. I don't buy it for a second.
People think in dictionaries, so just use one. If you are making a simple app and don't need transactions, aggregations, or multiple connections, then just use JSON in an S3 bucket or something. If you are going a step farther, JSON-based databases are quite feature complete these days. For monolithic business logic applications, relational databases are the right tool IMO, but they are used for every use case when they are absolutely not needed.
Controversial claim: Joins are a foot gun. It is so easy to make too many tables and mis-use unnecessarily complex table structures because it feels safe and "engineery" to do it. I don't know how many young startups I've seen that absolutely struggle with RDBM performance, and almost always they have gotten themselves into some horrible situation joining five tables deep with a spaghetti ERD and no clear pathway forward. It is hard to make the same mistakes with a JSON foundation.