Not exactly, tracing over the 3d is called 'rotoscoping', and has been used in animation for a few years now, basically hand-drawing animation over a 3d video. There are two problems with rotoscoping. 1. The cost, its not much cheaper than just drawing it by hand. 2. The effects don't compare to diffusion. If you pay close attention, you'll find that diffusion not only added facial expressions, it even added SHADING and crevasses to the dresses. That stuff is extremely difficult even for a human to do repeatedly.

Indeed, diffusion is superior to 2d animation, even in raw quality. Because diffusion will soon be able to produce illustration level pictures for each individual frame. Whereas 2d animation had to rely on detail-compressed simple artstyles AND keyframe-inserts to cut down on costs. Soon every frame will be a keyframe, and it can execute artstyles previously impossible to animate.