What you just described fits my definition of boring, which is some function of (time passed, individual at keyboard)

Cobol was (and for some, still is) exciting at first, but _becomes_ boring once you master it, and the ecosystem evolves to fix or work around its shortcomings. Believe it or not, even UX/UI testers can deal with and find happiness in clicking through UIs for the tenth thousand time (sure, last time I saw such Tester, was at around 2010).

This doesn't mean the technology itself becomes bad or stays good. It just means the understanding (and usage patterns) solidifies, so it becomes less exciting, hence: "boring".

But you can't sell a book with the title "Choose well-established technology". Because people would be like, no sht, Sherlock, I don't need a book to know that.