[honzzz]

Did you just assume 100% reliable HW+SW...

Why would you think that the parent assumes 100% reliable SW? Having SW more reliable than humans would be enough reason to replace humans with it. This does not seem impossible to me.

[Piskvorrr]

Well, the problem with current state-of-the-art flight automation is that it can deal well with routine, repetitive tasks. What it fails at are corner cases (cf. US Airways Flight 1549), and self-diagnostics (sensor readings are inconsistent with current flight profile, e.g. Air France 447). In such cases, what you need is intelligence, not automatics.

This makes your argument another case of "let's assume we have strong AI; then pilotless aviation is easy-peasy." In other words, one of your unstated assumptions is still firmly in the realm of science fiction.