Oh Lord.
Sand is already solid, as fragment of rocks.
Magma is a semi fluid? Right! But a semi fluid from what and what makes it a semi fluid? Answer: magma is molten rock, and the reason it is molten is heat, a kind of energy that we can find on fire. The manga doesn't says that smothers the fire. Says that it's stronguer, and by what o saw on google, there is no science backgrpund for this afirmation. Still, this is a manga, and not everything must work according tp our world.
Every new villain will be a new threat to Luffy, with new challenges. Today Luffy would destroy Crocodile, as most logias wont be a challenge with haki.
But I can't see Lucci or Moriah been a bigger challenge then Crocodile. Luffy could have a gear 3 against Crocodile, if he can touch him, it would be useless.
You're arguing semantic here.
Crocodile is not a Rock-man, he's a Sand-man, therefore, he's the fragmented version of Rocks. Sand may be solid, but it has no structure just like Water, or Air, therefore, it requires Haki to be attacked like it's tangible.
That's why when Luffy punches Crocodile, his fists simply go through.
The definition of a Logia is simply a fruit that makes the user intangible.
You answer your own question with your question, they keyword from Magma is "Molten" rock, more or less partly fluid. The thick fluid is capable of putting a flame out.
Magma does smother fire, that's the only way it can put out Fire, no one who does science can deny that. It would be no different to putting mud on fire, it'd smother the fire off oxygen, and therefore render the fire obsolete.
It's really not the case that Magma is superior to Fire in the sense that it burns hotter, Fire can burn hotter than Magma, irregardless, once it's deprived off oxygen by something that's part liquid, it ceases to be able to burn due to lack of oxygen - it's impossible for combustion to occur without oxygen - Ace is Fire. That is simply the reason Akainu was able to burn Ace, not necessarily because he was stronger, a matter of DF superiority similar to Electricity being incapable of conducting through Rubber.
You don't need to see Lucci or Moriah being greater challenges than Crocodile, the fact is:
- Crocodile was defeated without the need of Gear 2nd or 3rd.
Your rationale here would be like saying that Joker is inferior to Crocodile despite Joker needing to be defeated by Gear 4th, and Crocodile with no Gears.
And what do you mean
if Luffy can touch him?