One example of how Dr Ingham teaches the use of tea brews is with trichoderma – add trichoderma inoculum and proliferate the fungi in a brew when powdery mildew is present on your crop. Use the brewed organisms, sprayed onto the leaf surface, to consume the PM. Thats quite specific. I’ve heard Christine Jones share a similar sentiment to you – that in a general tea brew its probably the chemical signals of microbes that are “working”. Other explanations are pretty general, like covering all surfaces, consuming all exudates, etc. Might be important to remember how tiny these guys are, and that perhaps an environment on/under the leaf can exist where they will survive?