I believe the reason CV bombers do not have formations is their historic use. IIRC, CV bombers flew in much the same way as CV fighters, i.e. with a wingman, and in relatively small numbers, perhaps a squadron or two grouped together.
On the other hand, land-based bombers flew in MUCH larger numbers (1000 bomber missions, anyone?) and flew in a "box" formation, which is what I believe the three bomber set represents.
So, no, I do not agree that CV-based single-engined bombers should have the formation option that the land-based multi-engined bombers currently enjoy.