Ah, well said and very honest. I'll go over a bit of your points, if you don't mind. ^_^
-Katon has one of the widest scaling jutsus in Naruto, as you stated. In a battle, there's something called zoning, which basically means forcing your opponent to stay in certain areas so that you can manipulate him as you wish. With fire and earth, you can control the grounds, and with lightning, you can control the skies.
-You are correct about the diversion. Because it is also a wide scale jutsu, it can hide you, not to mention how dam loud it burns, blocking up any jutsus you may be hiding.
-Lastly, Fire is the best element to counter with. Say if you released a C-Rank Fire jutsu against your opponent's C-Rank Wind, then the fire would eat the wind, as you said yourself, and that makes the fire a B-Rank as a result.
Alright, I hope you learned a bit.
Proceed to come sit by me in this firecamp and observe the fire. Tell me how you think Fire chakra would flow in comparison to say...Earth chakra?
Also, what is fire's weakness?