You say PO-TATE-O and I say PO-TAHT-O...
If one wants to argue what constitues performance:
What kind of performance do you get in regard to gas mileage"
How does your engine perform in regard to emissions?
If you want to measure performance by "area under the curve", then you still are only talking about WOT, and EGR is not an issue.
If your definition of performance is to maximize power at all rpm/vacuum conditions, then indeed, EGR affects performance. On a road-race or autoX car, I can see this rather limited view of the word performance applied to good use.
On a street car, I think the broader view of all around performance is more appropriate.
Semantics.
It is documented that you get better mileage and lower emissions on engines with EGR and fuel injection that have been tuned for it.
I personally am fond of breathing, and even after I don't have to be emissions tested, I will keep my catalytic converter, MS my ZXT, and utilize a wideband and EGR for my daily driver to maximize performance in the areas of, power, mileage and emissions. No doubt I will bias toward power and mileage (since everything is a compromise something has to take back seat), but I have no doubt that what I end up with will pollute less than the stock EFI system.