It's still not a power up. He had to train for what's going to be his "power up"- greater haki flow control.
I've you are not able to tame it, it's pretty much even a drawback..
And going from overaverage haki control to greater haki control is also not something that has to be "awakened" through an extreme diff battle. He hasn't unlocked a new ability like control over his haki flow, he already was an advanced CoA user beforehand, he just got much better at it via training with Enma.
It's just a training tool.