About all this Logia nonsense, the assumption is that they are invulnerable unless they are forced into a situation where their assigned (fire, elec) antimatter/"element" (Ice, sand, smoke) just cannot exist. As a result, Ao Kiji most definitely is not untouchable because ice can be forced to not exist by raising temperature. Likewise, Smoke can be forced to not exist by dispersing it, electricity can be forced to not exist by dissipating it with a insulator, sand can be forced to not exist by making it into mud, fire can be forced to not exist by taking away the oxygen in the atmosphere. The only reason why Ao Kiji appears so strong to people is because his counter to his tolerability to weakness far exceeds Croc's, which is also much more in abundance (water…) than Kiji's (a very high temperature that he cannot immediately reduce to comfortable temperature where he can operate, lest risk being vulnerable while the temperature naturally returns to the desirable range)
If you want a comprehensive guide on DFs, especially paramecia, I've written one and I'm sure it's currently foolproof. Zoans and Logias (which also I have written quite alot about) are more straightforward though. Here's an excerpt from the essay. Terek, your df analysis has missed out a category. That would be Blueno's fruit. Unless you want to argue that it is the creation of something that makes things doorish. It's covered in the text yonder.
_Firstly, it is the body alter category. Those that fall under this category include Gomu Gomu, Sube Sube, Supa Supa etc. In each of these, the body becomes rubbery, frictionless and metallic respectively. There is no command over the substance itself, only over the user's body. In my personal opinion, I would say this is the weakest devils fruit, though it can help the user out in a pinch. This is the only kind of fruit that gives the human body new properties aside from Logia, but in this form, the change is permanent.
Secondly, there is the environment alter category. The only one I can think of is the Doa Doa fruit. It allows the altering of an object's properties when in contact with a user. The Doa Doa fruit seems to be the first of it's kind to me… Their bodies also will still be in human form, it seems.
Thirdly, there is the substance emission category. Users create an object from their bodies, but their bodies are not that object. Their bodies remain in human form. These include Doru Doru, Hana Hana, Noro Noro and Ori Ori. They create wax, body parts, the Noro photon and cages (of an unknown substance) respectively. Unlike environment alter, they create new substances and do not alter ones present in the environment.
Finally, the body change category. The users of this category retain their human bodies but are able to rearrange their cells to form a higher density or just a new form for themselves. However, all the while, they still are flesh and blood. Examples are Toge Toge and Kilo Kilo. The first one creates spikes and the second one increases weight. They are still in human form when their powers are in activation. Unlike Supa Supa where the user is steel, these are still flesh and blood although in different shapes and densities._