Not focusing on learning advanced forms of haki doesn't automatically mean weak haki or that your haki cant compete with those that do.
Doesn't change the fact that yes advancing in haki makes the individual stronger but again doesn't necessarily mean their base level haki strength is superior
Armament haki-
Not having armament barrier or penetration doesn't mean your armament haki is weaker than those who do
Don't think anyone believes this but
- Marigold having barrier armament doesn't mean her armament is stronger than sanji's
- Pica having full body armament doesn't mean he has better armament than killer
- Raisin coating his blade in hardening doesn't mean he has stronger armament than law
- Having a black blade doesn't mean you have better armament than garp
- The scabbards having whatever haki they got doesn't mean their haki is better than blackbeard's
Observation haki-
In the case of observation haki it is slightly different. Main reason being is yes you can just have better observation haki than someone else. This being because observation and armament working differently
With armament there's a clear step by step progress
Basic armament-> barrier armament-> penetration armament
With observation it's more like a tree with different branches. The different abilities being
- Presence sensing
- Emotion sensing
- Intent sensing
- Strength sensing
Like yes having future sight clearly mean you have better intent sensing than those without at the very least. At the same time due to their being different branches of observation doesn't mean you have overall better observations technically
Having future sight doesn't necessarily mean you'll automatically have the ability to sense a whole like fujitora, rayleigh, and enel have shown
Tho enel technically used his fruit to help if i remember correctly
Conquerors haki-
Like rayleigh explained to luffy when he first showed it off you can't train to strengthen it directly
The strength of your conquerors just depends on your overall strength
As for coating
When it comes to coating attacks it's most likely them appying the same rules as armament and its advanced stages. Infusing your armament and conquerors together makes it stronger
Yamato not being as skilled as luffy and kaido in armament is likley the reason why her and kaido's attacks made direct impact but not theirs
As for why or how sky splitting happens its likely just due to the raw pressure/strength of 2 extremely strong conquerors blast clashing
