I don’t think this would work this way unless the candle wall breaking is done in super slow-mo. Like sure, Luffy could break it, but given that his whole fighting style at this point is based on using elasticity and momentum, his fist would stop once he hit the wall.
See, one thing I love about the Gum Gum as opposed to the powers of rubber people like Plastic Man, Mr. Fantastic and Elastigirl is that Luffy is still using his normal human muscles to move. Those other stretchies can turn into a boat or a screwdriver or a flat plane because their power isn’t limited to stretching but bodily manipulation in general. Luffy can’t flatten his whole body without pressing downward on himself or being assisted by an outside force. Stretching out his arm is just like when you or I use our muscles to stretch out our arm, except Luffy’s bones and ligaments and flesh are unencumbered by having to stay in hard static positions.
My best guess here is that Luffy isn’t doing as strong of a punch as he would with a normal Gum Gum Pistol. Instead of stretching his arm back and then hitting with the combined force of elastic snap back, momentum and his own physical strength, Luffy is just sorta pushing his fist forward using the natural musculature of his shoulder and arm. Like, we have the muscles to stretch our arms out a good bit, but pushing them further results in strain that Luffy simply doesn’t experience.
It’s still very strong since Luffy is a strong-ass dude, but it’s less like winding up a punch and more like pushing someone you already have your hands on. Mr. 3′s low constitution makes it seem like a way harder hit than it is. Or maybe it’s just anime physics.
