As a curious scientist, and a chemist at that, I did some research into the chemistry of tea brewing. For black tea (which is all I drink) you need the water to be as hot as possible to dissolve the flavour chemicals out of the tea as they are not especially water soluble. Hence using freshly boiled water, pre-heating the pot and covering it with an insulating layer (cosy). This is also why you don’t put the milk in whilst steeping.
There’s a lot going on in the steeping process, and timing is important - too long and you start extracting increased levels of bitter chemicals that cause the ‘stewed’ taste.
Water quality is important - using hard water generates ‘scum’ on the surface which is unsightly, but the minerals in the water also affect the steep and the flavour. We live in a hard water area and always use water from a filter jug for tea.
Of course, each to their own.