Plot has devolved to become super formulaic at this point.
They always split up when they arrive at some new place, zoro gets in trouble,
the weaker crewmembers get picked on, and luffy does something stupid like falls asleep while everyone's getting their ass kicked.
Fast forward 20-30 chapters, crew comes together against some random enemy, and luffy finally wakes up to swoop in and save the day.
Literally the second they met the mermaid it was obvious she would get kidnapped.