I agree with what your saying. But, if you pronate a tad bit when you throw, you can put that pressure on your index finger to get the same cutter movement. Take a ball in your hand, 4-seam grip. Middle finger on the bigger horseshoe side. Now take your two finger and move them to the right, RHP so your the left side of your middle finger is on the edge of the big horseshoe. This is the grip. Your thumb shouldn't move that much, a little though, Now simulate the throw in your hand with the ball coming off and you can see that using the index finger and a little pronation, you can get the movement also. This also seems to be better if your more of a 3/4's arm slot.
Not for Mariano Rivera. :lol: [/i]