Why the Secret Spell Scroll system would have never worked.

That would stop crash duping yes, but if you found a way to rollback your character without crashing, you could still dupe.
This is how the supposed crashless dupe is claimed to work,even though it uses trading, which is already a save point.

No, dupes are all the same, whether they're crashless or not. They both involve rolling back. This one that was public is the same as the one that was public a few months ago. It just involves locking your character so that it rolls back when it's unlocked during the next server crash/check. Channel crash dupes involve the same method except it just crashes to roll your character back.