It is often said that as tea plants get more stressed, the taste of tea becomes bolder and superior.  Source of stress could be elevation, shading, and even soil conditions. 

In China, tea harvested in wild is often considered better quality than cultivated tea.  Wild ones have stronger flavor and potent?  Da hong bao is still the king of tea in Wu Yi mountain.   and many other wild seedlings are propagated, but the seedling is still considered the highest quality.

In Japan, they cultivate exclusively for high quality tea.  One saying in Japan, tea and chrysanthemum only get better as you give better care. 

Interestingly, the discrepancy is not only cultivation, but also types of tea.  Wuyi is known for oolong and Japanese green.  Yet, factors like seasonality and elevation tends to influence quality both in Japan and China similarly. 

Stress to the plant from elevation could cause devastating freeze, but low summer temperature can slow hardening of the new growth which greatly affect tea quality.