Well you have to remember that they are pirates. It would feel strange if they had better strategy prowess then the marines that is basically the one and only military in this world. Sengoku is supposed to be the most feared strategist we have heard of. And he has home field advantage.

Also Sengoku raised the claim of Whitebeard trying to make Ace the Pirate King. It's been a common theme that most of the old big name pirates from Rogers era look for the newer pirates to have their own era and that their role is now more of support. So if that is true then that would make even more sense why Whitebeard is prepared to sacrifice this much for Ace. Even though Marco has higher rank, he don't strike me as a Captain. He is more of a follower. And i bet that is what WB thinks too. Marco would be a good leader, but Ace will be a great leader. Ace have demonstrated a strong will many times and he has the same kind of charisma that Luffy exudes.