It depends what you mean by useful. Most humans are (at least at the moment) more versatile than even the most advanced AI we have. But you have to keep in mind that there are jobs with pretty mundane tasks where you don’t really need the intelligence and versatility of a human.
But speaking of efficiency, a human can do more useful tasks while AI is crunching numbers. But that is very subjective.
It depends what you mean by useful. Most humans are (at least at the moment) more versatile than even the most advanced AI we have. But you have to keep in mind that there are jobs with pretty mundane tasks where you don’t really need the intelligence and versatility of a human.