If a diver who is not actively exploring is routinely encountering visibility so limited that absolute fluency with zero-vis procedures for longer than a few body lengths... that diver needs to seriously re-evaluate their buoyancy.
The instructors I was referring to are active explorers, so that - in combination with the GUE mantra of beginning with the end in mind - might have played a part. With my very limited experience, all I have is conjecture, but I am guessing that percolation in less traveled passages, restrictions and maybe especially other divers/teams are very real risks of encountering bad viz or no viz. Newer cave divers might be less likely to encounter those kinds of passages, but they might also have a higher likelihood of screwing up the viz in a stressful situation, or of being in a part of a cave frequented by other rookie divers. Like you say, we were also told that in most cases no viz is highly localized, but knowing that you can make a complete exit of the cave blind would only make encountering any amount of no viz less stressful.
If you don't bother the bottom, it won't bother you and in many thousands of hours in the water and observing lots of divers around me every day I find that zero-visibility is not a thing that everyone needs to be prepared to deal with at any moment's notice.
Unless other divers in the cave disturbs the bottom. It seems prudent for me for anyone entering a cave to be prepared to deal with no viz.
Gear fails, though.
I've seen brand new hoses explode. I've seen second stages fall off. I've seen fittings come loose and wings fall apart.
I've seen lots and lots and lots and lots and lots of gear failures. But rarely have I seen true zero visibility for more than a few feet.
Absolutely. I didn't mean to imply that no gear fails, or that you shouldn't be trained to handle it. But multiple failures, or a failure leading to complete loss of gas (like a manifold failure) seems to be very rare. The point that was made, was that over a collective 90 years of diving and thousands of cave dives, they had encountered only a handful of failures like that. Failures leading to the loss of one post, like hose failure, were more common. Low/no viz were according to them much more common than any failure.
Yes, we need mastery of both. But the biggest shortcoming I see is just normal diving practices. Teamwork. Communication. Linework. The stuff we ALWAYS do. That almost everyone has some shortcoming on during every single dive.
That's what the most time should be spent practicing and discussing during class.
That sounds very much in line with what I was taught, especially if you add Finning Techniques, Trim and Buoyancy to that list. I was told many times that if a new cave diver gets in trouble, it's probably because of a breakdown of the fundamental skills. So to be fair, it's probably more accurate to say the message was:
Many cave classes spend too much time on complex failure scenarios and not enough time on the fundamentals of cave diving, including comfort with no viz.
Not some nonsense you need to do once for your instructor because it's a lonely, scary skill that, ideally, you are never, ever going to do again and barely remember the steps of if you do.
Hmm. I can only say that for me personally, it really reinforced the respect I have for line awareness. You might think it's nonsense, but I think psychologically experiencing "being lost in a cave without a line" even in a drill is something that can't be replaced with stern warnings or teaching strict protocols. And for an instructor, I could even imagine it being a decent screening drill, as you might argue that someone panicking or not being able to keep a cool head during that drill might not be ready for cave diving.
As for not remembering the steps, again I'm not so sure. Of course nobody knows how they will react in that situation until it happens, but excluding a mindless panic, the steps are quite simple and logical. The tie-offs are pretty obvious, to have any sort of reference, and then search in a pattern that fits the situation. What would I forget? Placing a cookie on the assumed exit side when you find the line? Stowing the light? Those are the only candidates I could think of, and while they might increase the risk of mis-navigation or entanglement, neither seem to make or break your chances of survival.