This is absolutely incorrect. The best thing you can do to enhance your tea-drinking experience is to buy good tea, and good tea is invariably brewed off the boil, usually somewhere between 170-200F, depending on the tea.[0] Higher temperatures will extract too much tannin at the expense of aromatics. The British generally drink shit tea and then add milk to it, which is why they can get away with brewing it at 212F.…
The guide explicitly says to use Earl Grey, which is a bergamot oil infused Assam. Both of these loose-leafed teas, as well as typical British loose-leaf blends such as English Breakfast, are brewed at 100 C, and taste awful (bitter and slightly mealy in the mouth) when brewed at a lower temperature. A cheap blended tea such as you'd find in a tea bag of PG Tips are much better at brewing (in seconds!) from non-boili…
Also, the OP was incorrect; there are no tannins in tea. Bitter & astringent flavors in tea are caused by a different group of polyphenols (primarily catechins in green teas and theaflavins/thearubigens in black). Polyphenols bind with salivary proteins that reduce salivary lubrication. Since both temperature and steep time determine what gets extracted from the tea and how much, it's important to get both right to get the flavor right.