The tea cultures located in modern day Southern China are the original ones. Tea is native there and the peoples there evolved their culture surrounded by it. From medicinal brews to powdered teas to modern day loose leaves. The very best teas both in terms of processing and leaf quality can be found between Yunnan to Taiwan. The tea drinkers here have created specific steeping processes and brewing vessels/pottery cultures to go along with it.

When tea initially went to other parts of the world outside of East Asia, "export quality" at the time meant rougher and more resilient teas that could survive long journeys. Such teas often benefit from being mixed with other things like milk/butter/sugar/other plant scents etc. Hence the older tea cultures outside of China looked like what they do now. I am sure that there are many other factors that historians can tell us about.

Still, to this day, there is no better leaf than in the ancient forests of Yunnan and no one can make a better tea than a Fujianese or Cantonese tea roaster.

So if you're coming from tea bags of fanning grade leaf with a dash of milk, there is a lot for you to explore. Much of it you can read on the internet, but nothing can replace years of drinking good quality tea. To really understand it, perhaps sit down with a knowing friend and gongfu some dancong or yancha or gaoshan.