That is what "destroying the SAM system" means. A SAM system isn't just the missile battery, it's the entire defensive scheme within which the SAM battery exists as the shooting arm of said scheme. In a WW3 scenario, what's liable to happen is that NATO is just going to accept a different level of what constitutes "acceptable losses" then it did even in Vietnam for both SEAD and strike missions.
The impression I got from your initial statement is that destroying an air defense system was eliminating the batteries. If I misread you than so be it.
The real issue though is that in terms of density, the North Vietnamese, Egyptians and Iraqis had has dense an air defense system as anything the Pact had deployed anywhere in Eastern Europe (indeed only Moscow was more heavily protected) but yet their opponents successfully carried out missions at will with losses that were acceptable once counter tactics were developed and at the height of their being tested, their opponents were able to do whatever they needed to do in terms of missions.
It should be noted that initial losses during Linebacker II and in the October War were high (probably at a level we would have seen in Germany) but those losses dropped off very quickly. Losses in the Gulf War were minor (in terms of sorties, aircraft and missions carried out). While the Egyptians and Iraqis never really seemed to get the hang of the interceptor portion of the air defense mission, the PAVN Air Force was very good considering its small size.