But there's no reason to not take it seriously, it's still what happened in the manga.
Marco and Jozu are indeed tough to deal with defense wise. They both only lose in MF when distracted and unable to defend themselves, and Marco's defense is reiterated again like a decade later in Wano. Imu's powers are the same, it's not early arc PL's to say that no one in the GV 6 can even do anything to Imu. That's a major plot point.