The thing about squeezing the tea bag is that it leaches more tannin into the water -- you're also increasing the caffeine content, as a result, but the tannin is what makes it bitter. Higher-tannin red wines are also rather bitter tasting, IME.

As for the blasphemy of mug/bag/instantly-hot water... one does what one has to do. The important thing is getting your morning cuppa! :)