The 35 spline is stronger than the 33 spline because of diameter. The 33 spline is 1.37" dia., the 35 spline is 1.50" dia. There are ways to cut shaft splines to make them stronger than others, but the big difference is the diameter.35 spine axles are stronger because of two reasons more contact area and Ryan from TCS also explained that the way he can cut a 35 spline makes them stronger then a 33 spline
To a point. A 35 spline shaft can be made to have more twist than a 33 spline shaft, but it will take more power to twist it. The 35 spline shaft (designed properly) will also take more twisting before failure (cyclic fatigue).Becuase the bigger it is the less it twists. The less it twists the more it beats up other things.