It was confirmed long ago by Oda that Haki has many levels. It isn't as simple as three abilities that offer the same level ...
Ultimately, the God Valley Incident reframes Conqueror’s Haki not merely as a weapon, but as the purest expression of human ...
The Straw Hat pirates will have more than just two conqueror's haki users in One Piece. Some, however, have more chances of awakening it than others.
Luffy has a huge haki upgrade ahead of him in Elbaf. This upgrade will allow him to fight against immortals in One Piece.