I kind of agree with your assessment, it would even speak to the popularity of document DBs coming up around the same time. However, I would argue that the decline in deep RDBMS integrations is exactly because of their excessive complexity. Modern software development methods left them behind because their change velocity is awful. This is doubly apparent when you look at features like TFA is talking about, exactly because it's extremely complex to stand up, manage, and make changes to.

I personally left in the era of ORMs exactly because it let me build systems in high-productivity languages and frameworks, but also because the cost benefit of RDBMS integration just wasn't there. The DB is absolutely the highest-risk place to put logic in any stack, if something goes wrong _everything_ breaks and it's the most difficult place to fix things.

I don't know what the future looks like for DBs, but I think we'll continue to see them become even more transparent. Devs just want to persist entities, and integrating at the RDBMS level is a slog.