The index finger is not the strongest when it comes to gripping, FFS is correct that the middle and ring are the true gripper fingers. You can ask any martial artist that uses grappling and they will explain how the various wrist locks and such work with just the two "grippers" and the thumb. You actually have a weaker grip when applying pressure with the index finger.
-W
Learn so much on this forum. Great people here. I think my finger idea is out of date even for climbing. As the Tewks vid sinks in though it is sitting strange. That's a strange looking swing if you ask me