Both have a place in shaping your expectations of the viva.
Stats can give you an outline, a pencil drawing that is a reasonable shape of the viva experience.
Stories can help to colour in that picture, give you details to help you see what vivas are like and how they feel.
Both have a place: your outline might vary a little, you might paint with different colours, but listening to stories and putting them together with the statistics for viva experiences should give you a useful blurry picture for your viva.
Squint and maybe you’ll see your future! Ask for advice, ask to hear about experiences, and then see how they make sense with where you are. No-one needs to go to their viva with a blank page for expectations.