Rotoscoping has its place. It can save a lot of time/money for scenes with complex motion and can produce good results, but overreliance on it does tend to produce worse animation since it can end up being constrained to just what was captured on film. Without it, animators are more free to exaggerate certain motions, or manipulate the framerate, or animate things that could never be captured on camera in the first place. That kind of freedom is part of what makes animation such a cool medium. Animation would definitely be much worse off if rotoscoping was all we had.