I think you are getting at a wrong conclusion.

Praxeology as defined by wikipedia, "is the deductive study of human action". Deduction is deeply rooted philosophy, mathematics and logic. A very valid way of scientific reasoning.

It is a different way of doing science, than the "scientific method", which uses observation and quantitative methods.

The Austrian school derives consequences from human action, allowing to describe what can happen in an economy, qualitatively. But their method doesn't allow to make quantitative statements, which makes it "useless" to politicians wanting to change the economy.