Again, Enel said it, and Oda has given no reason to doubt it. And you yourself gave the parallel example of Mr. 1. It's not like there isn't another Paramecia like Luffy's. And I think that Luffy's power isn't that he became like rubber. It's more that he gained the ability to stretch like rubber, and thereby the properties of rubber. Just like Mr. 1 didn't gain the ability to turn into metal, he gained the ability to turn his body parts into blades and they get the properties of metal when he does. And also, Logia abilities can be turned off. Luffy is always rubber. Buggy can always survive after being chopped up. Alvida is always slippery. Luffy's ability isn't really that unique among Paramecia abilities. Certainly not unique enough to warrant being classified as a Logia, I think. He fits into the Paramecia criteria alot better then he fits into the Logia criteria. Besides, a Logia doesn't just become that element, they can produce it, control it, utilize it, manipulate it. Luffy can't do any of that. And again, rubber isn't really that sort of element. I know that Logias don't just go by the Aristotelian elements, (earth, fire, water, air) or even the "RPG Game" elements" (grass, rock, electricity, that sort of thing.), because they have smoke, gravity, sand, ice, etc. But those are all still a certain type of substance. A type that at least SEEMS sort of elemental. But rubber isn't like that, really. There is a better case to be made for Mr. 1 being a Logia user then Luffy.