Take an underexposed image and push it 5+ stops and the 6D still looks pretty good while the 5D3 looks terrible. When I go look at the actual measurements from DXO it says that the 5D3 is rated at 11.7 for DR and the 6D is only marginally better at 12. Something is not right there, or there is a huge difference in whatever scale they are using between 11.7 and 12.
And surely this is the point Canon CPS are making. Measure DR and the 5Ds will stay roughly in the same ball-park as other current sensors. But you'll be able to lift shadows better through lower read noise.
There is little more to it than that, which is why Canon have not made a big fanfare for it.
But perhaps more back to the point. Canon wants to keep Canon people using Canon. They're not rolling out anything other than iterations to sensors - no step change. For many Canon shooters, that's enough to upgrade based on all other elements. For some, it may be enough for them to change.
It it were solely about quality / DR, then we'd all be using MF bodies. It's about what you have, what it might cost you to swap and what Canon needs to expend it order to release something that will hopefully make you buy a new body, but at worst not defect.
I think Tom Hogan is correct in that matter.
Everyone has to decide whether current DR with lower read noise is enough for them given the other things the 5Ds brings and the Canon ecosystem. If not, sit this one out. But please, don't expect any step changes in the 5d IV or 1Dx II. Not happening...
My only disappointment in the announcement is that nothing ships till June, rather than April. YMMD.