I think this current arc shows the difference between dealing with an Yonko and dealing with a top tier Shichibukai like Doflamingo. The gap that Big Mom and her crew has over Doflamingo and his crew is huuuge (with Gear Four Luffy apparently being useless against her), so if we consider that Doflamingo is the 2nd strongest Shichibukai (might not be the case with this new one who alleges be Whitebeard's son) and that Mihawk operates mostly alone, I don't see the Shichibukais standing up to even one Yonko, even more when the likes of Crocodile and Moria were already defeatable by pre Time-Skip Luffy and his crew.