Rhys, while I don't want to spark a huge debate about this, I don't have a problem with however other leaders choose to assess would-be leaders, I'll explain my point-of-view...
Some years ago I had to 'fail' a would-be leader not once but twice, as he simply couldn't find the way out of Pi Chamber. This despite being given plenty of time to do so, even on the second trip!
This is really the only tricky bit of routefinding on the entire route. I am sure that had we been going in the other direction he'd have found his way around with no problem.
All too often in debates about fixed aids and so on on the escape route, people come up with a lot of hypothetical 'what ifs', but I am sure that had my would-be leader had to 'escape' a rising stream with a party of inexperienced cavers he'd have got to Pi Chamber and then stalled, so I had to turn him down. This despite the fact that he was a mate!
Personally I also think it is valuable to assess how would-be leaders deal with the climb into Lowe's Passage (formerly Lowe's Chain but now rigged with a rope) as this is something that can cause difficulties for some.