Hi, I am new and this is the first comment that I post
I think that ALL the crew of the King of Pirates must have the haki of armament and the haki of observation.
First of all because Robin Nami Brook Usopp Chopper and Franky will gain in power and will be less of a liability in battle. And the Haki can be combined with their fighting style
Usopp : cover his ammunition with armament Haki and with the observation Haki he will be able to aim better, dodge and anticipate attacks etc... and also protect himself to avoid fracturing his skull
Franky : could cover his arms, body and even his ridiculous giant robot with the Haki of armament and also cover his missiles with Haki so that it is more powerful and resistant but also to protect himself and avoid futile injuries. The Haki of observation will allow him to aim better with his laser, to foresee better attacks but also to anticipate and dodge the enemy attacks
Brook: the same thing better aim and anticipate, dodge enemy attacks but attack enemies more quickly and effectively with the Haki of observation and that of the armament will allow him to make his attacks more powerful etc. ... But also protect his bones
Chopper : Hand to hand fighter Haki of observation and armament required no need to explain why
Nami : armament Haki to protect herself from enemy attacks, I don't know if it's possible to cover the lightning with armament Haki but if it's possible it will make her lightning more powerful. The Haki of observation to dodge the enemy attacks but also to aim better with his lightning and to establish better strategies to attack and also to follow the speed of the enemy to defeat him
Robin : in addition to having spent 2 years with RA and knowing the word Haki (she is the first one to say Haki when Luffy uses it to put down 50000 fish men and it is also her who on Punk Hasard explained to Franky what the Haki of armament was used for) she knows what it is. And not learning the Haki of observation and armament at RA's side is very stupid if she hasn't learned it. It will make her attacks more powerful and she will be able to protect herself from enemy attacks. Observation will allow her to dodge, attack quickly etc...
To conclude, the 2 Haki can be combined with any fighting style. Having the haki has only advantages! And it is necessary that ALL the crew has it especially if they fight the crew of Blackbeard who has devils fruits, nothing better than the Haki.
I don't understand why the rest of the crew would do an expection by not having the Haki, it's the crew of the future of the PK they all have to know how to use it especially when random of Kaido's crew and even Big Mom's crew have the Haki of armament.
If they don't have it, the crew is a joke, I'm tired of it. That the power of the crew is based on Luffy Zoro Sanji and Jimbei because let's be honest if we remove these 4, the crew in terms of power is worth nothing.
If Luffy Zoro Sanji and maybe Jimbei fight the admirals then the rest will have to fight the vice admirals and in the navy to be a vice admiral you have to have the 2 types of haki, I don't want to see vice admirals being defeated by vice commanders who have no haki.
The same thing for the crew of Blackbeard, I don't want to see this crew of devils fruit eaters being defeated by vice commanders who have no Haki
The same goes for the Shanks crew, friendly fights or others, no desire to see a crew that is specialized in the 2 Haki be defeated by a crew without the 2 Haki
I just want that Luffy's vice commanders have the 2 basic types of haki ( without ryuo and without the observation haki of the future ) just that. Realize that Caribou who is a logia user is super weak, a punch in Haki armament is he is defeated, in Luffy's crew you have to call on minimum Jimbei to defeat him because he is a logia, even Chopper could defeat him but as Chopper doesn't have the Haki armament he can't. It's a shame for a Yonko crew
They are still the vice commanders of a Yonko and the future PK !