Looking at it from a different side, if Shanks indeed stopped Kaido so that he can't assist WB at Marineford it means that he intentionally protected both Luffy and BB and allowed them to develop throughout the story for some reason. And i mean a disingenuous one that serves Shanks himself by starting a proxy war that involves every stakeholder. Like someone waiting for an ancient entity to awake before snatching it away.
If Oda seriously goes all out perfectly tying every question mark roaming around Shanks', he would be the most morally questionable, best written character that came out of this show.
If Oda seriously goes all out perfectly tying every question mark roaming around Shanks', he would be the most morally questionable, best written character that came out of this show.