The argument that "they don't need it" also doesn't make sense... We have lots of characters who has both but never used it... But the SHs, they can use it anytime in the story...
It's funny that Oda unlocked Zoro's CoC but the rest never unlocked one... Well, Robin arguably...
The thing is, there are lots of Haki users in the NW... They're pretty much left out... It may not be needed to be strong but it's a necessity for their own survival... Do note that there are times that having a Haki is a necessity (i.e. to sense an imminent danger or an extra protection against petty offenses or Logia-based attacks...
It's funny that Oda unlocked Zoro's CoC but the rest never unlocked one... Well, Robin arguably...
The thing is, there are lots of Haki users in the NW... They're pretty much left out... It may not be needed to be strong but it's a necessity for their own survival... Do note that there are times that having a Haki is a necessity (i.e. to sense an imminent danger or an extra protection against petty offenses or Logia-based attacks...
Frankys tech is stronger than haki of powerful new world pirates
Robins clutch techniques is stronger than haki of powerful new world pirates
Haki is just one power system that can be easily offset with those who use other power systems. Saying they all need haki is like saying they all need devil fruits.