Re: Relational DBs never went away.
I agree with your points in general. SQL has some massive advantages when dealing with structured data.
It's a lingua franca, rather than requiring you to learn a query language for each product.
Also, while setting up the tables may not be super easy (and why should it be?), you can do pretty much anything you want with the system afterwards, as long as your query skills and the performance are up to it.
However, even outside of web-by/scaling/distribution problems SQL does have at least one massive Achille's heel - self-referential data, like parts-of-parts and modelling a car engine for example is not a good fit for the standard relational model. Configuration data is another case - defaults, options, overrides - they make sense in JSON, less so in SQL.
I suspect a good solution might involve co-opting graph databases on occasion. And I rather like the liberty that comes with sprinkling in some JSON data into Postgresql columns, without having to shoehorn every problem into SQL-type ERDs.
i.e. I don't think MongoDB and the like are so hot outside of some particular, albeit broad, domains, but I like the fact that we are experiencing so much innovation in alternative ways to organize data rather than being forced to use SQL for everything.