Brachiosaurus is one of the worst ancient zoans for combat if we discount the max durability. Yeah, he can tank damage, but he can't dish out damage to sanji either. brachios are slow and have restricted movement. There is no way fat balloon queen is keeping up with Sanji.
This is what i want to say, because Brachiosaurus might had big "defense" stats *if this was a game.
So you need big "Attack/strength" to take down Queen. In this case, because Sanji might didnt have a big amount of damage, unless he cooperate his diable jambe + raid suit in the fight.
This is why i said Sanji
might able to attack Queen, but Queen
will able to tank sanji's damage all the time
Who did Marco fight in MF? Marco will have clashes. Expect a Marco vs. King clash. But that's it. Defeating a major opponent 1 v. 1 is another issue....
Remember, the alliance is outnumbered. Zoro is wasting all this time fighting SMILEs. Marco brings muscle to the game. That's what he did in MF.
This is my point, if Marco need to fight in this arc, he has to fight King 1 vs 1.
If we gonna see Marco & Zoro fought Against King, thats bring a disrespect to Marco's name as a YC1.