The guy is an idiot...
1. He complains of some optical vignetting, some of which happens a lot with wide lenses in particular, and especially zooms. This is nothing new and not related to the camera at all. Okay, it might be made a little more obvious by a digital camera, than with film in the past. But there have been "center spot" filters available to correct this on film for decades, very pricey. A 58mm Hasselblad Center Spot will set you back $500 for example.
But you don't need to go to that expense with 5DII. The camera has peripheral illumination correction to help with optical vignetting. I doubt the writer of that article ever discovered that feature on the camera. That involves reading the user manual or other learning resources, and actually wanting to know how your gear to it's full potential.
2. He complains of corner/edge softness. Well, you know, when you blow up an image from a 5DII to 100%, that's equivalent to about 5 feet wide. That might be fine if you were looking at the image as a print, hanging on a wall, from a "normal"viewing distance of 5 or ten feet away. But when you are sitting 18" from it, staring at your computer monitor, you'll see every little flaw. I'd also question his particular copy of the 17-40L... But realistically it is the cheapest wide L available... And it is a zoom. Wouldn't be surprised if he had a $25 UV filter on it, to protect it from air touching the front element, or something like that. And did he use the hyperfocal distance to take those shots he shows as examples?
Anyway, anytime you are working with new gear you have to spend some time learning it's optimal settings and uses, if you want to get the very best out of it. Chances are he'd have probably gotten better results if he'd backed up a few paces and used a less wide setting on the lens, which looks to have been easily possible to do in the example images. Or just get a smaller format camera that crops off the edges and corners of the images (the 10-22 and several other crop specific lenses are pretty amazing... he's holding the FF camera and lens to pretty high standards!).
The problem with the Internet is that anyone can "publish" their thoughts, even when they are ill conceived and idiotic. This is a good example of that. Not that the 5DII is a "prefect" camera... it's not. But blaming a camera for the inherent faults of the lens and/or how you're using it is just plain dumb.