In single hand mode sure, but it still got used in sideways NES style a lot. I do think the combination of curved and flat is awkward, though. Considering Nintendo's portables for the last quarter century and the wiimote all had very flat edges and even the Wii U Game Pad is pretty flat away from the rounded corners, I think MDave's mockups go too semicircular, like the child of an SNES and a Sony portable.
I'm happy to explain my reasoning for using curves instead of flat sides on my mock ups, as I think its important for informing people on a comfortable handheld to hold:
Curves are far and away more comfortable in the hands then flat sides and squared off corners.
SNES controller was a step up in ergonomics over the NES, thanks to its curved sides. Good thing too, because of shoulder buttons it introduced.
The Wii Remote was designed to look like a remote, hence the flat sides. You don't rest your fingers on any corners of the Wii remote because there are no shoulder buttons.
The Vita is more comfortable then the original 3DS, thanks to its curved sides.
Those with larger hands will know the pains of gaming on the GBA SP.
Taking the size of the Wii U gamepad in comparison to the SNES controller, yes it does have rounded corners. Not squared off corners that dig into your fingers like the GBA SP and 3DS do. 2DS have rounded top corners where the shoulder buttons are because they don't have to worry about making it flat so it looks nice folded as the 3DS does.
I don't think you will find many that disagree with me on those things.
Last but not least, an important observation:
With the exception of the GBA Micro: Nintendo have always done curved sides/corners when shoulder buttons are on the controller, and when there isn't hinges taking up space on those top corners.