I already said that I don't have dietary restrictions also biscuits are typically referred to as being made with biscuit dough, not biscuit batter (at least where I'm from). I think discussing the differences between a dough and a batter in this context though is straying too far from what we're actually talking about so I don't particularly want to get into that.
I don't understand why you're putting quick bread in quotes so I'm asking sincerely do you not know what I mean when I say quick bread? As in something that's "leavened with a chemical agent rather than a biological one" such as baking soda/powder instead of yeast? Because this includes cake (and brownies and cookies even), I will change my case to be more like: Most people I've met in the US aren't wrong when they say they like muffins but it would be more specific to say they want cupcakes. In my opinion, we often put enough sugar into the muffins to cross the line into cupcake territory. Since they're both quick breads I'd argue cupcakes are muffins but not all muffins are cupcakes.
It's like my roommate kept telling me they like pancakes and so I'd make pancakes and they didn't like them because they were too thick. By the time I had thinned the recipe down enough for their liking I was actually making crepes, which are a type of pancake. They weren't wrong by saying they like pancakes but they would have been better off just admitting they actually like crepes and not what is generally thought of when someone says pancake.
I'm not trying to say that if you reduce sugar it is unchanged. I am saying that quick breads are very lenient with how much sugar can go in them while still maintaining good mouth feel, especially when the recipe already has a considerable amount of sugar as do many recipes that cater to modern US sugar addiction.
Plumb lines are used to find how off center something is from straight up/down. I think this is so you can know which side the tree naturally wants to fall towards and work with that