Personally, the whaleship is no longer a challenge to me and I can't remember the last time I failed a mission, even without a full team of rainbows.
Do you have any Solar Node generator girls on your team? The initial hit from a whale cannon does wonders.
Which helpers are you choosing? Nowadays people with 200k+ strength can be easily found and as far as I know, those are the best for the whaleship missions.
The earlier missions, where you need to battle on-deck first are harder than the later ones in my opinion, since you can get your units grinded down. I can't remember if there are any requirements to do the later stages, but if not, maybe try those.
Are you equiping every member of the team with levelled equipment? Since the max battle power is the main deciding factor, these come in quite helpful.
Name: Volarmis
DMM ID: 317568967