I am having the very same issue PLUS this additional one....not only are my lines ragged when using the lasso tool with my pen tablet, when turning the preferences on as shown below, my calibration is thrown totally off for my stylus. As soon as I uncheck the 'high precision tablet input' box, the calibration is corrected.
Like the OP, I am an illustrator and used the lasso tool in Photoshop in creating my artwork to create fluid shapes, fill and mask. Now the edges are so horribly choppy that I am needing to go back to my old Photoshop program to create in as these irregular lines will never fly with my clients and frankly, I wouldn't accept the work in this state either.
I've attached a screenshot for you to see the choppy edges...