Never was confirmed, Queen would kill off everyone if Marco not step up, Marco always stop him.
So he take for so long both at once, you see yourself if Marco not step up Queen would kill Hyo and co. So it make sense that Marco take on both. Marco didn´t yet use his full hybrid version or even awakening, he also not use haki yet. Bro he was impressiv asf with dominating both King and Queen this chapter, two strongest commander of Kaido, Marco should take the respect.