The taste is just plain dreadful. Not only is it bitter, the whole “sweet” part doesn’t even taste like the usual sweet you think of. Like lemonade, yes it is perfectly sweet. Soda beverages, THAT’S sweet. But TEA, awful. And it’s like no matter how many sweetener packets you put in it, it doesn’t at all help. It’s one of those drinks where you might give it another chance if it’s available thinking it might be better but it always lets you down.
If the tea is bitter you’re using water that is either too hot or too hard, or both, or you’re using over oxidized tea leaves.
Sweet tea (at least in America) is generally made with black tea, which is made by oxidizing dried tea leaves. The level of oxidation is (in part) what determines the quality of the black tea. Some brands (like Lipton) use the lowest graded tea leaves they can get because it’s cheaper. Which leads to more bitterness and off flavors.
All that said, I generally agree with you that sweet tea is awful. Though I’d go a step (or several) further and say that adding either sugar or milk to tea should be a crime punishable by being drowned in the disgusting swill you made.