It's true that making iron daggers is more efficient than making iron armors, but that does not extrapolate to higher tier items. As you move up the smithing tier, the value of the items go up dramatically. And the experience gained is roughly proportional to the square root of value created, or value added. So making one Daedric Armor (Value = http://forums.bethsoft.com/topic/1367340-anyone-not-use-smithing/3200) and improving to normal legendary (added value = 3200) will generate about same experience as making 35 iron daggers. If you wear fortify smithing gear, you can add 6400+ value to your armor for the cost of 1 ebony ingot, which will add roughly the same experience as 43 iron daggers.