Whether or not young people can discern how quickly society changes isn’t relevant to the argument. The argument’s premises tell us that the amount of value given to the advice of elders changes based on how quickly society changes, which can support the argument’s conclusion whether young people have this ability or not.

The argument’s focus is on using the amount of deference to measure how fast society is changing - the other reasons for that deference aren’t relevant to the approach.

This provides the missing link between value and deference. If (C) were to be negated, there would be no connection between value and deference. The premises about value therefore wouldn’t support the conclusion about deference.

The argument is only concerned with how we can use deference to measure the rate at which society is changing - reasons for why advice might not be useful or there might be a lack of deference aren’t necessary.

The argument does not need to explain the reasons why young people either do or do not value their elders’ advice - the focus is only on how the amount of deference shown can be used to measure how quickly society is changing.