Earlier quoted context omitted.
Don’t know about the US system. But I can imagine it can happen, at least in the UK system which I’m farmiliar with. External examiner who is in a related, but not same field for example. Or they’re just a buddies with the advisor and only give softball questions etc. The defense in the UK is not seen as a big deal, I don’t know anyone who has failed.
I can't imagine someone who isn't very familiar with their dissertation successfully defending here. Also to even get to that point were the advisor thinks you're ready to defend would require constant back and forth your advisor. Then committee is going to grill you. And finally the vast majority of dissertation defenses end with recommended changes. It really would require full time devotion on the part of the ghos…
I guess I’m skeptical that any qualification is 100% effective at evaluating/training (but that possibly says more about my own biases).