The advice from the experts like Jamil Z, John P, Charlie Bamforth, and classic brewing texts is that water above 180 F will extract undesirable tannin flavors from the husks of the grain. The extraction occurs at the point of contact. Any grain husk that is raised above 180 will begin to extract these tannins, the amount of extraction per husk will be proportional to temperature (higher temp = more tannins). It does NOT require that the entire grain bed be elevated. However, the more of the grain bed that is elevated the more tannins will be extracted.
This tannin extraction is also a function of gravity, and pH. The lower the gravity of the water surrounding the husk the more tannins will be extracted. Further, the higher the pH, again the more tannins that will be extracted. Note that pH and gravity are closely related, in that the lower the gravity the higher the pH will rise. The exact relationship between pH and gravity is a function of grist (darker grains tend to help keep the pH down), and water composition (higher Carbonate levels will raise the pH more quickly for the same grist).
The 200F water will raise the top of the grain bed above 180F almost instantly. Further, as the water drains into the grain bed it will raise more and more of the bed above 180F. How much ultimately gets elevated above 180F depends on the ratio of sparge to mash water. But, I would guess that, at least, 1/3rd of the bed ultimately would be above 180F.
So, the magnitude of the tannin extraction and therefore the taste perceptibility of it depends on:
1. Your specific recipe (lighter beers will be more susceptible)
2. Your specific water profile (high carbonate beers will be more susceptible)
3. Your sparge to mash water ratio (a higher percentage of sparge water will be more suceptible)
So, if you were trying to make a kolsch, with high carbonate water (>50ppm as CaCO3), and 3:1 sparge:mash water with 200F sparge water I think you would end up with a beer that didn't taste good at all.
On the other hand, if you are making a robust imperial porter, I doubt you would be able to tell a difference.
To be able to tell with any two beers you should do blind ABA taste tests. 2 of one beer and 1 of the other. If you can consistently pick out the "single" beer, several times in a row...then there is probably a difference. If several people can do the same thing...then there is very likely a difference. AB testing is easily susceptible to bias.
In the end, you are right. But, how much it matters is a question answered by the above.