Nice. This is a basic result in the SKI combinator calculus. https://en.wikipedia.org/wiki/SKI_combinator_calculus

I have 30 years of software development experience. I've worked on projects using Waterfall that were resounding successes. I've also seen abysmal failures from Waterfall. I've also seen quick success from Agile and abysmal failures as well. The successful Waterfall projects, the customer knew exactly what they wanted, they were willing to pay extra for quality and management was stable. Agile is perfect when you don't know exactly what you want, and you're wanting to rapid prototype. Maybe develop a minimum viable product. The problem is that once it looks good, everyone who's not a programmer assumes it's finished and becomes unwilling to invest in reengineering the asset for long term maintenance. All the shortcuts, and bad practice compound upon themselves till it reaches some maximum sustainable size based on the entropy in the code base. The later maintainers of the system are now in a pickle. Clear separation of concerns were most likely not followed and now the monolith becomes the beast that must be fed.

The real issue I have with Agile is not the method itself but that all too often management uses it as an excuse to cover it's own lack of management. "I don't have to do all that planning and crap--We're AGILE!!!" This inevitably leads to tribal worship of aforementioned monolith. Agile is not an excuse for lack of management.