That was literally Marco´s aim, he was keeping the people on the alliance´s side safe, while keeping two YCs busy, healing people, healing himself, taking damage for other people, the list goes on.
Pre-TS Zoro could not do anything to prevent Jabra killing Usopp because Kaku did not allow it (and Kaku was at best equal to Zoro, more likely weaker overall), and Kaku also did not use his strongest arsenal to keep Zoro busy at the time, Marco was keeping someone equal to him and someone close to him busy while also providing Chopper with assistance and prolonging the virus to take effect as long as possible.
Yet his stamina loss is somehow only prescribed to King, which is utter nonsense.