@leth
There are multiple problems with assuming Japanese green teas can be brewed just as well using a gong fu cha method, or that Japanese green tea quality can be assessed using the same methods used for Chinese oolongs.
These teas share a common horticultural ancestry but that is where the comparisons should stop.
Perhaps foremost among these differences is that the tea varieties have been selected for different properties, including brewing methods and flavor compounds.
Japanese tea growers selected tea bushes via vegetative propagation knowing that the resulting tea would be brewed at a lower temperature. They looked for bushes that produced novel flavor compounds that are attractive to the Japanese palate. Some of these flavor compounds come at the expense of increased bitter compounds in the leaves. This is especially true with varietals with assamica genetics (inzatzu) from crossbreeding. The more assamica genetics the more unique the flavors and the more bitter the resulting tea.
As I mentioned earlier in this thread, novel flavor compounds often come hand in hand with bitter compounds. Incidentally, this is why Dancong teas, with their unique flavors, are often bitter and/or astringent.
It wasn’t always the case that Japanese tea bushes were vegetatively propagated.
Seed grown Camellia sinensis-sinensis dominated sencha production until about a hundred years ago (zairai). Each bush on a hill produced leaves with different properties. When harvested en masse the resulting tea was good but not spectacular. You are unlikely to get consistency and novel flavors in a harvest like this. HOWEVER, you could brew the tea in boiling water with little to no bitterness. Early sencha was in fact boiled, not steeped. This could be done largely because the tea was seed grown and not select for genetics that produced novel flavors.
While Chinese tea is not seed grown and now uses vegetative propagation, there are not many varietals that were crossed with assamica bushes (and the few that were were done by the Japanese in Taiwan). The characteristics for varietal selection was generally different in China that Japan. Flavors were chosen for the Chinese palate and many were selected from ages old seed grown patches that did not have assamica genetics.
Generally speaking, more emphasis was placed upon terroir and processing than was placed on breeding programs.
If we just deal with the genetics, there is no reason to think you could gfc a sencha as a means to prove it is high quality, as you might a Chinese oolong.
