I think that funnily enough, the "semantic diffusion" itself is an example of how such things happen. I wasn't aware of that label and certainly will not be adopting it to my vocabulary. Sounds like a very complex way of saying something has changed its meaning.

Agile existed in a vacuum as a manifesto, then it existed as a driver for cults/zealots of the ideology, then as a de-facto process, and now it's just watered down to something execs repeat when they want to say "our company isn't like a regular stiff corporation, but something more adaptable than that".