If I can butt in. I am a former cabinet maker and it is a fairly simple job. Use a marking gauge to score a line parallel to the edge of the bat. With a tri square and marking knife/pencil/craft knife score across the grain to the edge. This should form a rectangle around the damaged area With a 1 inch (or wider) chisel remove the damaged area so you have a rectangle. Remove the material so you have a flat base (dead easy in a soft, straight grained material like willow). Cut a slightly larger rectangle out of the donor bat and glue in place. The key to this is to make some angled blocks to go in the jaws of the vice/cramps. Then remove the excess willow with a sharp chisel/knife. Finally sand flush.
For a slightly better repair, undercut the edges of the rectangular recess and cut the same chamfer on the 2 corresponding edges of the donor piece.
Although I agree in principle in what you've said. There is one slight issue I can across when I did the exact same.
The face of a cricket bat is pressed and then further knocked in
The donor bat will usually be pressed and knocked in
When you make it slightly larger, and then sand down, you sand away the pressed part.
You then end up with a soft corner off the bat, basically unpressed, knocking in will harden said part, but it then sits below the rest of the bat as its compressed.
What the solution is I don't know.