Whatever mate, only clarifying what the guy that actually flies them said. His outfit can directly compare the 77W to the 789 so I'd take his word for it....
Oh and he never said 25 tonnes payload was the maximum either could carry, only that he was comparing them equally with 25 tonnes each.
Why don't you ask him how much payload a 789 can carry over 14 hours, how much fuel it burns compared to the 77W?