The pilots did not train for a specific root cause of a fault. They trained for a symptom (uncommanded nose down), and the procedure for that situation was unchanged.
> extra burden to quickly determine if something else is wrong
This isn't an extra burden. Pilots aren't doing root cause analysis for failures while they are responding to them. They are trained to try actions in a specific order until something works. It's not like the checklist used to have one action on it and now it has two - the solution in this case was a standard action on the standard checklist.
Pilots do not look around, say "ah, electrical short in elevator actuator" or "ah, bad angle of attack sensor" and then take a single action.
