The artist should be doing this already!
I could see this getting prohibitive when creating animations for example.
BUT, with that 2x effort, you're getting a significant improvement in visual quality. The alternative would be the Donkey Kong Country option: model the character in 3D (easily 10x more effort than flat 2D animation, with a much more expensive work force and software), bake in the lighting, and generate gigantic animation sheets. Your asset library will explode in size. The games that have done this have tended to employ significant compression on the images, which can negatively impact visual quality.
And technically you could export the sprite sheet with however many frames you want (and be able to lower and increase the number easily) while still getting the exact same results as the Sprite Lamp solution. And of course artists could go in and manually make any changes they want.
It's interesting hearing the perspective of the artists. Thanks.
Also there are major stylistic advantages to drawing it by hand. Check out the baked-in motion blur on Sonic's feet in this sprite rip of Sonic 1: http://www.spriters-resource.com/genesis_32x_scd/sonicth1/sh... a while back there was a 2.5d Sonic game, and its motion had a lot less impact because no attempt was made to replicate the motion blur.
Plus of course if you're just drawing it you don't have to worry whether or not it actually makes sense - a lot of the more stylized cartoon characters are VERY hard to build spot-on 3d models of, because they're full of weird abstractions that only make sense in the 2d plane.
And finally, some people just don't like modeling stuff in 3d.
(I'm an artist and ex-animator.)