I'm not sure I can agree about modern political theory. The vast knowledge gained from reproducible experimentation makes a very good case for causality. In fact, countless theoretical breakthoroughs have been elucidated by experimentation. However, experimentation in political theory is severely limited in scope and predictive power. I'd bet my life on the valence of carbon based on atomic theory, but never on any prediction of a political theory, no matter how it was derived.
The tests take longer and it's harder to run them in parallel, but it's just a slower version of the same steps.
I think that is an argument that cannot be proven, as you could always fault the experiment or the time allowed. It's not that I think that political theory isn't important or worthwhile, but without demonstrable reproducibility, it's just fundamentally different to something like physics.