Let me ask you this, If Kidd and Law didnt ''beat'' BM who was going to? Plot allowed them to take those hits. I know you guys will never take the difference in circumstances into account though.
Maybe Oda considers Kidds story to be done or not that relevant anymore so ofc Shanks will do that. Point is BM had both beaten down on the ground, on their backs with both of their crews crying and begging her for mercy.