Temperature, length of brewing, water hardness all affect the taste.

Boiling water gives the tea a bitter taste. Trying brewing gyokuro with boiling water in front of a Japanese. Both the Japanese and the tea grow bitter because of it. The effect is very prominent.

Houjicha and bancha are low end tea. (Btw, are they even considered green tea?) Do whatever you want with them. It's like choosing the best glass for a table wine, it doesn't really matter.

Black tea, on the other hand, is more forgiving in brewing.

Tangentially, how popular is green tea in the UK? It seems quite niche?