During the timeskip Luffy learned the basics of armament and in wano learned the basics of the more advanced forms
The admirals might be a good showcase of a mastery of each form. Based on aokiji and kizaru akainu might have the best mastery of internal armament. Which is also fitting considering akainu > kizaru > aokiji
Borsalino definitely has the best mastery of barrier armament. With him being the one to teach sentomaru it with his being even better. He might not use it offensively as much but he has extremely good defenses using it. With how high his mastery of it is he probably has more advanced techniques with it too
If aokiji and kizaru have a higher degree of mastery over the 2 earlier forms of armament haki imo it could make sense that akainu is the best at the last step. As for what type of advanced techniques he might be able to do with it honestly i don’t really know