As I said, fell the holding tree. Not for the inexperienced, not the faint of heart, not the less than fleet of foot.
Dropping a hazard tree that just fell of it's own accord and hung in a nearby stem, I've handled many like that. I have never had to do so but once from my own hung fell, but more than a few clearing up after another's poor work. Not to say I never hung a tree

. Most often it was firewood thieves who failed in their attempt at felling a roadside tree. I'd get the call then.
Jim, I think that advanced "C" class might have merit, but the trick is finding some way to test for it. I ended up taking on, not all for sure, but many on my Forest. I'm not sure how that came to pass...just a case where I managed to survive a few, so the phone kept ringing and I learned something from each one, and the rep gets built.
But to train someone to that level of skill, intuition, and frankly, brass balls?? I don't know how that could really be done.