> the number of years of a monk's seniority is the easy and fairly-reliable gauge of a monk's authority

Authority, or expertise?

Authority requires either enforcement, or widespread recognition, or both. The government has authority because it has the ability to use violence. Doctors have authority because most people view them as authority figures.

Does the average Buddhist say "that monk has X years of seniority, so I'm going to take him by his word"?