While I agree speed would be the major advantage of Ishida, some of the Quincy techniques appear quite similar to the abilities of Organization XIII member Xigbar. Xigbar makes use of two gun-like weapons which he is capable of rapd fire with and using his power of manipulating Space to change the trajectories of his shots and open up wormholes to allow his shots to directly hit his opponent if he's at a distance. Lke the Quincies, Xigbar is also capable of speedy movements and reaction time. So facing Ishida would probably get Sora thinking of some of his opponent's tactics to be similar to Xigbar. And if Sora and Riku fought that kind of opponent, then Ishida would be no different from the major foes they've confronted.