By that reasoning there is a flaw in the process at Ruger. Ask a serious AR guy about his barrel and whether individual testing is important to him. He'll tell you who does and who doesn't.
I can't and won't argue that point. There is a flaw somewhere in "A" process, which allowed poor manufacturing of that gun.
As far as barrel makers go, smaller shops do more end testing, because the owner is generally owner operator, and therefore all processes are confned to one or a few personnel. Regardless, end testing is still the less efficient way to improve quality over all, and guarantees problems to be discovered after-the-fact, and after the process has been out-of-spec for a long period of time. This also results in higher manufacturing cost due to waste.
For example, by relying upon end inspections, three, five, or mabe fifteen handguns may make it down the assembly line before a problem is discovered. At that time, the process has varied yet again, and the QC expert is not sure where to start.
By measuring the variances of the processes, the out put is almost always guaranteed.
This is the last I will comment on QC, as I don't wish to high jack the thread. If you're truely interested in QC, read
Out Of The Crisis By E. Deming; other readings by Juran are also suggested.