Who needs dpreview. We have distortion charts here at TDP. Here's a 16-35 vs. TS-E 24mm comparion.

Also, I'm really not sure if the Samyang will be expensive. Their 35mm prime is as sharp as the Canon L, but a fraction of the cost. Some of that cost savings comes from not having autofocus, or electronic aperture controls. I think I've read that TS-E lenses are manual focus already, so perhaps the price difference will be less for the the tilt-shift lens, but I'd still expect a healthy discount.