It could be that the fletched shafts would have a bit more lift...
i've personally prefer a slightly weak spine over too stiff because its more forgiving to a less than perfect release. When your spine is borderline too stiff , you will often get too much strike plate contact by not getting completely to full draw, or have a less than perfect release, and have it kick the tail to the left as it makes contact.
Something that really needs to be said , and not often mentioned, is that carbon shafts have a weak and strong side to them that is often overlooked, or not even checked before bare shaft tuning. If you put a carbon shaft on a spine tester and rotate them 90,180, & 270 degrees i believe you will be shocked how much difference there is.... I've seen guys pulling their hair out trying to bare shaft tune every shaft in their new dozen shafts and cant figure out what is going on.... I would strongly recommend testing your shafts and matching up the spine closely on all your shafts. Then you can simply bare shaft tune one of them before cutting them to length...... Food for thought.... Kirk