One thing that gets omitted when talking about making a good cuppa is the water. A good cup of tea needs water with oxygen. Water in a kettle that has been boiled one or more times loses some oxygen. People often leave this re-boiled water in the kettle and just top it up and boil it again for their next tea.
If going to boil the kettle for tea making, I empty any water left in it, before putting freshly-drawn cold water in. Never water from the hot tap that's been through your boiler or stored in a hw cylinder. If you follow this basic rule, you will have a better, brighter cup of tea. Also, let the boiled water stand for a minute before pouring from the kettle.
Yes, IMHO, adding the milk to the cup first is wrong if brewing with a bag in a cup. However, I like strong 'builders' strength' tea, and always squeeze the bag to get the last tanin hit. As I like a half spoon of sugar, this reduces any bitterness.
Like the Op, I'm not keen on PG Tips. I used to use Typhoo, until they reduced the amount of tea in the bags, which meant that I couldn't get a cup strong enough for me. I use Tetley now, as there is more tea in their bags and it's a reasonable everyday cup. Twinings English Breakfast is also good.
Think I'll put the kettle on after all that!