Can it also be argued that having hatchery strays in the system is a good thing?

Both wild and hatchery steelhead and salmon stray from their home spawning rivers. In the past when there were huge numbers of wild fish everywhere there were comparatively huge numbers of wild strays. That is what gave what we consider native fish their genetic diversity, spread the run timing out, etc. Am I correst in saying that a "river A" hatchery fish is just a severly dumbed down "river C" wild fish? After a generation or two of spawning in the wild they are essentially wild fish right? Why are the hatchery origins of these strays a problem unless we can define an what an "excessive number" of those fish are?