Long thread so I'll give a quick take:
There are some serious developments in progress that Canon seems to be slow to react against. The Exmor sensor for one, and much of the mirrorless market for two.
That said, these new Nikons are not "game changers". They are very nice packages, and one that indeed should elicit a competitive response from Canon. But overall they are just more of the same nice sensor in a nice dSLR. While the new D5 may do some things better than a D4 or D810, there are not entire ways of working enabled by the new D5 that simply could not be done before. That is what a "game changer" is.
And yeah.....it can be frustrating when your brand has cameras that seem to be uncompetitive in several categories. But Nikon sucked hard for a long, long time with their DX only CCD sensor approach and they survived. And if you see a camera you must have, buy it.
Finally.....if you think the 100-400L was a lousy lens, you are nuts. 