How can I make a quick bread mix less sweet?
You can change the flavor profile of mixes by adding more flour to cut the sugar. In the case of quick breads, I would suggest using self rising so that your quick breads will still have enough leavening. 

Another way to cut the sweet would be to add ingredients that are savory, such as nuts or vegetables.  Depending on the mix, additions could vastly change how sweet it tastes.  They also make mixes that have reduced sugar in them that you could try.  Some of the health food mixes and specialty diet mixes (things like gluten free and vegan) might be more up your alley.