Yeah the reward was small with Just Defend, you'd only get a sliver of life back, and I think you'd recover a few frames early, but possibly not enough to attack (or at least do what you wanted to do)...
If you're talking deflecting in 2d vs 3d, you're right to some extent... It's easier in 3d fighters I believe because of the frames in general... Most 2d fighters have moves with faster frames, whereas in some 3d fighters, the frames are generally slower per sé. By far, Tekken had the fastest moves for a 3d fighter, with VF behind it; I think they're about the same now, since both games have gone through dramatic changes...
Deflecting/Repelling in LB was harder because the window was smaller than a 3d parry/deflect/repel... It looked slow because of the animation in general, but the whole animation wasn't the actual deflect itself, more like the small window to parry and then the recovery portion, which was shortened if you guessed right... I hope that made some sense...