I don't have enough hands-on experience regarding Luma's deadliness, but I will take Sozo's word for it. Also Luma is UTTERLY ADORABLE OMG WHERE CAN I FIND A PLUSHIE OF THIS STAR CHILD?!
I find it endlessly amusing how, in the world of Smash 4, gigantic and fierce-looking characters like Bowser, Charizard, and Ganondorf are consistently destroyed by little kids, electric rodents, and star babies.
It's "Nintendo logic" at its finest.