So basically what I have achieved with this thread is rounding up all the various opinions I've heard on this topic that confused me to begin with, and gathered them into one place to read one after another. Perfect.
Training is definitely a factor. I know some moots at UBC bring on the top experts in the country as coaches who then have connections to various practitioners in the city that act as judges during practices. This isn’t true of all our moots but in this regard, name brand of the school plays a big part.