I don't know what you are trying to add. Yes, if testing would have uncovered this and the release was put out without that testing, then someone is incompetent

I don't know what you are trying to add. Yes, if testing would have uncovered this and the release was put out without that testing, then someone is incompetent. But my point is exactly that the "egregiously visible failure" as you say may not have been visible at all during testing. You seem to think that by "not possible to test all paths" I mean that "logging in" was not tested. That's not at all what I mean. I mean that even for basic user flows, there is an astronomically high number of possible states and external inputs such that, taken together, something that worked fine during testing may stop working at some point thereafter, or in the hands of the actual users. Latent bugs are called latent for a reason.