The reason why unevenly tightened shoes from one wheel to the next does not cause uneven braking is because when the tighter one receives enough fluid to move the shoes to the drum, there will be no braking action until the rest of the wheel cylinders receive enough fluid to move their shoes to their drums.
Most pulling while braking is caused by worn front steering components in my experience, but gets blamed on the brakes until a brake job is done and the pulling problem still remains.
Bottom line: Don't look for the magic bullet. Inspect and repair everything.
