In the One Piece series, haki is a power system that separates the strong from the weak. It is not just about haki only ...

Rayleigh has great control over advanced forms of both Armament and Conqueror's Haki. Although not as strong as an Emperor in his old age, he can hold his own against just about anyone in the series.

Observation Haki is one of the most powerful abilities ... not everyone may possess a Future Sight as advanced as the Emperor's. This raises the question of whether this ability helped Shanks ...

The fact that Sabo was considered to be the Flame Emperor, and given that he is Dragon's Number Two, fans should not be surprised to see him utilize the power of Conqueror's Haki soon enough.