What? Your grammar is egregious dude. But yeah your comparison of 5ARI to castration makes no sense as there are way too many differences such as an increase in serum T, tissue T, E, and the many various feedback loops in the endocrine system. That comparison you are trying to make is an atrocious oversimplification.
Already addressed this. We do not even have the ability to test the many intricacies of the endocrine system, another example being the measurement of androgenic activity in the intrafollicular unit, which most likely differs from scalp values.