[JunkDNA]

Some care is needed to not conflate "overhyped" with "useless". There are plenty of software engineering technologies who haven't lived up to the hype because expectations were set way too high. They are however extremely useful.

I was taking a master's level database course at the time of XML mania and we spent a massive amount of time on XML because the prof felt XML + XQuery was going to displace traditional relational databases. There were numerous reasons why this didn't happen, but a not insignificant number of people bought into it. Some database-y things are possible with XML, but you'd be crazy to replace a massive schema with it without good reason.

OOP is another great one. It is incredibly useful to write OOP code. However, the promise at the beginning of the OOP mania was that you could "snap code together as easily as Legos... even normal people will be able to write complex software!". OOP has certainly helped make code more maintainable and fostered a lot of code re-use, but the ease described by the early hype was hugely off the mark. It turns out it's really hard to write super-reusable code such that you can use it "as-is" in situations the original authors never envisioned.