I didn't take photos of my failed parts, but here is one of the Andrews countershaft third gear. Notice there are very slight radii at the bases of the dog teeth. The stock gears have absolutely sharp, zero radius corners in these areas. The only way to reduce stress in these areas would be to machine a very shall undercut radius as you describe. You can well imagine the difficulty in doing this just by looking at the photo.
The Andrews gears are of superior quality to the stock gears, and not just for this reason. Superior materials, heat treating, and held to tighter tolerances.