@AppleSauce:
Logia's have way more possibilities with their abilities than a Paramecia.
Magellan, Luffy or Mr.1 or Mr.3 are limited to the product which comes from their own bodies and have certain things they are not capable of doing when you compare them to Logia's.
Logia's Go way beyond what only their bodies are capable of doing.
They effect the environment around them with just being there.(Ace at Drum)
Or they effect it for years if they go all out.(PH Admirals fight)
The possibilities of a Logia having varieties of different powers are WAY more than a Paramecia who are limited to certain things of the element they control.
While Logia's have full control over such element. The Possibilities are limitless with a Logia.
Ace is seen using different types of flames to fight.
Kizaru turned his light into a Solid Sword.
Akainu rains down Meteors from the sky.
Aoi kiji can freeze the air with his breath and turn grass blades into a sword.
Croc can Turn everything organic or not into dust.
It is true what you say, but they still "only" use their element.
Ace's fire is fire, I don't see any differences except scale and form of his attacks? All that seems to change is the intensity.
Kizaru forms a light-sword, but it is still light, the same "material".
Akainu rains down meteors, which are simply cooled magma fists
Same with Aokiji, it is still ice.
I admit Crocodile's is a bit special, but Paramecia's can do things that are considered "out of this world", even by One Piece standards.
See it like this, if Kalifa's df would be logia, she could produce soap bubbles without limits and turn into soap. She could cover vast areas with it - but it would still be simple soap.
Now as a paramecia, her bubbles gain an "out of this world" aspect: the soap robs her victims of their physical strength and might turn them into soap dolls.
Both options have their obvious advantages, but for the gas-gas fruit I think a paramecia would be better suited. Sleeping gas, gas that causes hallucinations, gas that downright kills you, "out of this world" - paramecia super gas (similiar to Magellans Venom Demon) etc.
If he is a logia he would be limited to simple gas - at least this is how I see it.