Both of em are peak human condition and Grayson much smaller then bruce. Size does matter regardless what you think. Plus Grayson is more athletically gifted then bruce is, I mean Grayson parents was very athletic its in his genes he came out of his mother doing somersaults lol.
I think its goin be somewha lihh dat young justice episode when he had to make a decision. I forgot wha episode it was but considered wha had happen it can be a good thing or a bad thing dependin on the person point of view.