I have to point out that many troubled projects I have worked on have decided they needed to implement a system that started to strongly resemble a home-brew RDBMS.
This invariably does not turn out well, as they are generally buggier and less fit for purpose than most RDBMS systems.
RDBMS systems do in fact have their issues — but like a lot of tools — one needs to be well versed in their strengths and usage.