I agree with this, it'd be an effective way to demonstrate the power scale, plus he's seemingly the only yonko the would beat them and leave them alive.
Probably while throwing them a party in honor of the effort...
Actually thats a good point - Shanks is probably the only Yonkou which would be able to display his power with killing off characters. Doubt Kaidou or Big Mom would let them get away with it xD