It looks like AC is using the 450 seat 77w to ATH, which has same number of PY seats as number of J seats in Rouge 767, but the 777w holds additionally 24 J pods and 179 Y seats, so perhaps the high density means AC can make the route work combined with the stronger demand.
28 J, not 24. They have used the 77W to Athens in the past. Doubt there is trouble filling it at the moment.