Big blades have noticeably tighter slip characteristics which means that they "lock" more suddenly (and efficiently) to the water than blades of lesser area. This means, I believe, that they permit a steeper build-up to the rower's peak pull force which could lead to sharper loading of the rower's back.
The "cure" for this could be to compensate for increased blade surface by increasing the flexibility of the shaft since, as we see, indications are that one pays no penalty for greater oar shaft flexibility (9.).
Flexibility has the secondary effect of changing the apparent fore and aft rigging; having the effect of moving the torso bowward with respect to the pin during the stroke.
To the degree that the shaft bends it will also change the angle of the blade relative to the water.
Who will be the first to try out this idea?