Technically, it is. If not an actual hard code, if you know how to read a scan tool, it should have been caught. You can monitor EGR performance by watching the EGR temp. voltage signal. It *should* be about 4.5v and decrease to below 1v at high engine speed. You can also watch the voltage readings to see the performance of the rear oxygen sensor compared to the front sensor. I'd suspect a system lean code (P0171 or 172 depending on which bank it is) would have been generated too. But this also brings us back to competent diagnosis. If you work on cars, in this case Subaru's, they should know to check the EGR valve if they have one. EGR's are becoming a thing of the past as Nissan/Infiniti has stopped using one for a few years now. We get the same results with variable cam timing and software programming.
Shopping is shopping. Doesn't matter if it's a good butcher, accountant, or mechanic. Ya gotta look around. If your trapped with only one dealership for your brand of car, maybe you should have bought something more mainstream? Why buy a brand XYZ if there is no one, or only one place, for repairs?
Not all the time, or in Gryzynx's case, but the consumer can be the problem too....