It's unreasonable and a bit naive to think that Canon's latest FF camera won't be compared to its chief competitor.
So because of one metric - slightly lower DR than in the D800 (which is utterly unimportant to most potential users and which in any event can be significantly equalised by the right conversion and PP decisions) - you're suggesting that the 5D Mk III is somehow a "lesser", uncompetitive camera; and that anyone who sees its strengths (of which it has many) over the D800 and prioritises them over the D800's DR "advantage", is being naive?
1. It's not slightly lower and believe me when Canon had a SNR advantage, when it wasn't even as large as three stops, you hardly went around calling it slight.
2. Calling it utterly unimportant to most potential users is going too far. Sure for many shots you won't need it and some people might never need it, but it's not that hard to come up with scenes where it helps. And again you hardly called the high iso advantage Canon had something utterly unimportant.
3. No you can't significantly equalize it in post any more than you could make a 2004 Nikon DSLR closer in SNR performance to a 2004 era Canon, well, not unless you are disingenuous enough to only apply careful PP to one camera's output and not to the others.
4. Just because people call it out for low ISO performance doesn't mean they are slamming every last thing about the camera. It does tons of things body performance-wise than the 5D2.
And it does a few things better than the D800 (6fps in FF mode; video without color moire problems and with less aliasing and with a good 1.5 stops better SNR (although it's also a bit softer and some say they used really cheap audio amps again); it's too early to say but it might have better AF, I read various things though and i haven't heard from any people I have a good sense where there are coming from chip in on the matter yet and I haven't tested either one myself; a bit more dynamic range a super, super high ISOs; personally I like the Canon UI much better; it matches mount to a nicer overall set of lenses IMO).
D800 is a beast though too, a lot more MP for more max detail and reach, on paper at least the metering system should be better, has a built-in emergency flash, built-in intervalometer, superb maximum dynamic range, doesn't have silly little things like autoiso crippled.