The recommended CP is there for a reason, even if you have less than 1 point, you WILL get a debuff in form of damage+defense+health reduction.
So, if you pass the stage where there's 2k+ of cp difference, that's already a flag. You know there's stage record right?
It's a difference story if it's only less than 500 cp difference, IF & only IF you have right team composition where only dolphin/whale can pull that feat off