Since no one does pure waterfall, everyone does Agile.
Even this essay encourages that interpretation: "Everyone in this group had deep experience writing software, and they were all looking for an alternative to documentation-driven, heavyweight software development processes that ruled the day."
Did that "everyone" include Mac development in the 1980s? Or Amiga development? Not from what I've read of the history.
Did it rule the day for the development of gcc, the Linux kernel, Perl, or CPython? No.
I pulled out my 1996 copy of Steve McConnell's "Rapid Development." Page 271 says:
> In addition to providing explicit support for morale, Microsoft gladly trades other factors to keep morale high, sometimes trading theme in ways that would make other companies shudder (Zachary 1994). I've seen then trade methodological purity, programming discipline, control over the product specification, control over the schedule, management visibility -- almost anything to benefit morale.
The Zachary 1994 citation is the book "Show-stopper! : the breakneck race to create Windows NT and the next generation at Microsoft" at https://archive.org/details/showstopperbreak00zach . A quick read (search for 'documentation') shows Windows NT development did not use a 'documentation-driven, heavyweight software development processes'.
And of course oodles of small software projects in the microcomputer and early web era were written with no formal software development processes at all.
This "rule the day" statement must therefore be interpreted within a narrow context.