Well, I am sure that pros using Canon, and lots of users using Canon, could easily afford the competition, say an equivalent Nikon system. Still, somehow, they don't, they must be masochists, or blind, for not seeing the light. So it is not a matter of money, so your comparison is meaningless in this context.
Unless you mean that pros using Canon should dump their kit for more expensive systems, like Leica? But then, how would they shoot Copa America or Euro 2016? Or the coming Olympics?
Indeed. Anybody thinking that it isn't possible to take amazing pro level images with Canon gear has a problem with reality. The % of pros shooting Canon depends on the domain and country, but it is overall probably well over 60%.
It at least tells us that Canon equipment is good enough and dependable and new generations will only make that better.
Some combinations of body and lenses are not just good enough, they are the best available, such as the 200-400 f4.
Now, that is rarely, if ever, thanks to the level of performance of the body, it is typically thanks to the level of performance of the lens.
And this is the reason why Canon still owns 60% of the pro market, photographers like their lenses and don't think (right or wrong) that Nikon's lenses are as good or better enough to make it worth a costly and time consuming shift.
Pro photographers are overall busy and tired, why take a risk unless there is a clear competitive differentiator?
I personally think that the AF of the D500/D5 may be such a differentiator for some applicatins but I am sure that they will soon realize this by themselves if I am right.
Cheers,
Bernard