Luffy: Basic CoC>Two year training with it>CoC coating>Advanced CoC
Zoro: CoC Coating>Advanced CoC
Sanji: Direct AdvCoC
I am hoping Sanji will find his own answer for regeneration instead of AdvCoC, but he's gonna make these two look like clowns if he pulled it off.
Zoro: CoC Coating>Advanced CoC
Sanji: Direct AdvCoC
I am hoping Sanji will find his own answer for regeneration instead of AdvCoC, but he's gonna make these two look like clowns if he pulled it off.

The protagonist is shown to struggle to master a power but when the power became trivial storywise, everyone can get it with less effort:
Goku need extensive training and emotional damage to reach SSJ => Vegeta « only » need extensive training => Son Gohan after intensive training jump from no SSJ to SSJ2.
This also applies to opponents:
Goku had a hard time to beat Freezer => Trunks beat to Freezer level fighters in 3 heartbeats.