[g_p]

As you say, different departments and institutions have different approaches, but I'd definitely emphasise that outside of Europe (where I've seen more ceremonial "exams"), there are still robust and vigorous "final" oral viva exams used.

In some European universities, the outcome is such a foregone conclusion that the candidate's family is laying out the buffet, peeling the cling film off the plates, and unboxing the champagne bottles as the "defense" begins.

In the UK however, I've never seen this. It's generally a small room with candidate, an internal examiner, an external examiner from another university who is an expert in the field, and a convenor to record the minutes of the examination. The outcome is by far from a foregone conclusion.

A good student who is an expert in their field, is well-read and up to date on their work and the surrounding literature will perform well and have little to fear. Someone who hasn't written their own thesis, or didn't really have an understanding of the area, and thus isn't really an expert, will have a very unpleasant time, and will likely be failed, or be sent away with major corrections to be completed to the satisfaction of the examiners, possibly including a full oral re-examination.