You like to poke faults at things eh?Oda failed and gave luffy a weak ability, so he decided to screw the plot and do what he wants.
Luffy made the power incredible.Oda failed and gave luffy a weak ability, so he decided to screw the plot and do what he wants.
Didn't Jinbei say that Blackbeard was attacking more DF users and gaining powers?Luffy made the power incredible.
Also, while the details haven't been revealed, it is generally believed Luffy uses the heat of Gear 2 and friction to ignite his arm.
Luffy has one Devil Fruit, only Blackbeard has two.