Usopp isn't very top tier in fighting and he got Observation.
It really matters on the individual.
Some people lean more to one haki and some can master both of the basics.>>115341928
I haven't watched Mao-Mao too extensively, but
Mao himself might be leaning towards Armament.
Adorabat and Badgerclops feel like the type that go by their lives without getting haki.
Bit more Devil Fruit mechanics, you can only eat one fruit to gain one power. You cannot eat another to stack or replace powers. If you eat a second fruit, your body disintegrates into dust. Old lore was that your body is destroyed by two demons fighting inside you, but that was an in-universe old wives tale.
Also there are no duplicates. No way for there to be two fire users or three "scissor-men" at the same time.
When a fruit used dies, the fruit power then reincarnates into a normal fruit that matches, changing the normal fruit and giving it the devilish looks.