That's not at all what usefulness means in that context, we talked three times already about it together. It doesn't need to scientifically testable to be useful. It simply needs to be useful in other spheres of inquiry than itself. For example, mathematics is useful for in a plethora of domains that go from engineering, mechanics, physics, sociology. history, accounting, cooking, philosophy, etc. Not all of these domains are scientific and you don't need to "scientifically test" mathematics themselves nor could you really since mathematics is a model of reality and, frame of analysis and a conceptual language. The greater the wisdom, the more profound a revelation, the more use it has and the more impact it creates.
What I demand is for guru to show the worth of their philosophical teachings by demonstrating its usefulness thus it's wisdom. Also, many guru make causal claims for example that their teachings can produce certain extraordinary results which are quite tangible and thus can be studied and analysed in a scientific manner. That's the case of the two I have helped expose as charlatan. One claimed he could fight off people without touching them and harming them with the strength of his spiritual energy. Another claimed he could heal various hailment up to and including deadly disease and otherwise uncurable ones. Both those claims can be debunked.