The argument of "They focus on Zoro" isn't valid at all.
I think Zoro>Sanji, but even if it wasn't the case, they would still focus on Zoro because it's pure logic.
They thought Marco was dead (which is a bit stupid but that's the case according to Queen), there's only Sanji left and 1HP Zoro. Zoro is curently 1HP, Sanji is still ok. If they focus on Sanji, Zoro will get back to 100% soon and it will be 2v2, if they kill Zoro (which is supposed to be easy since he is 1HP and Marco is "dead") it's 2v1.
Pure logic, doesn't mean anything (and yes, i still think Zoro>Sanji, that's not the point)