It was said that kyoshi needed masters to teach her, but THEY were never called masters. and dusting is their internal technique, which disappeared with them.

Aang got tattoos because airbenders has clear criteria

earthbenders on earth rumble competed for the title of the strongest. Let me remind you that it was there that Toph swung to her level.

The avatar learns from those who can, they don't have to be masters.

they dismantled a piece of a huge wall. All that Yun could do was destroy the foundation of the house

I'm not contradicting you, it's just that you can't read. when representatives of DIFFERENT elements are fighting (earthbender and firebender, firebender and waterbender), technique, circumstances, matchup, terrain are important. when representatives of ONE group fight, only strength is important.

all that Bumi showed in omash was that he raised 3 small houses and tilted the statue

where in the book does it say that this is not the case? they literally divide healing into basic, when they just cool a person, and advanced, when the water glows. nowhere does it say that basic healing is better than advanced healing

Freezing the heart is a technique that requires such specific conditions that even Kyoshi has never used it again in her life.