Don't get me wrong, I'm going for one of the top trades and so a higher mark was always expected to be required. However, the test itself is ridiculously difficult.
I actually know someone who joined the RAF as an Engineer about 6 years ago. They just tried a mock version of it again now, having heard I didn't pass it with flying colours (as they had done easily) first time around... and they couldn't believe how much tougher it was in comparison. To the point they themselves didn't pass to the level required in order to do, what they actually do, in the RAF.