thanks for once again for adding to the reference material
TB: The wide cutting edge is very necessary in order to hew and cut away wide chunks of material.
Also remember that the wide axe's weight adds to the momentum of the stroke, and will increase the work accomplished, something like a fly wheel on a motor.
The curvature of the blade doesn't mean that you only use the centre part of the blade, this is only noticeable on the final pass along the log's face, and it is at this time that you really need that curvature to do a good job and leave a nice texture to the surface.
As you are hewing, the wide cutting edge is being used to its fullest, for instance if you rough score 12" apart you can clean away easily the 12" width, and you really move along.