Via the high quality of content here in this forum, I recently learned the elements in a dual-element water heater are never on at the same time. The top one is controlled by a switch that disconnects the bottom one during energization. So then, having a second element would not make your heater more powerful. Rather, it would seem to me that a second element would only be most necessary inside a tall tank where the upper element could get things started and then pass the job along to the lower element that would finish warming the water in the tank and take care of smaller amounts of cold recovery water that never make it to the top. Overall, I suspect a second element in a smaller tank would seldom come on at all and mostly act only as a backup in the case of failure of the first element if the upper switch will still let it come on.