We'll have to agree to disagree on your argument that the AAT was a "mistake", Sandy. Many pilots' careers and life's passion have been saved by the AAT. "Traditional courts" don't do merits review.
The AAT isn't perfect - far from it. Under-resourcing doesn't help. Stacking it with political mates doesn't help. But the underlying concept is sound and has proven itself as such, more often than not.
In the mid-2000s the coalition government said it was going to abolish the AAT. Didn't happen. The current government said it was going to abolish the AAT. Won't happen (though maybe a name change will). The "traditional courts" would be completely overwhelmed if they were given jurisdiction for the matters currently considered by the AAT.