After the initial clash where the three realize it's futile to chip Imu's puppet down without targeting him directly in Mary Geoise, they will try to dip away.
Xebec will hold Imu off while the other two escape.
Garp really doesnt fit into this tho
Obviously we dont understand imus ability but from what we seen in elbaf, he needs to appreantly to defeat the strongest fighter to domi them.
The strongest fighters out all of them is xebec, who likely domid
Also it fits with harald who also very heavily looked domid and is xebecs equal