You could use all that mana to cast tons of Elves, or simply pay a huge amount into one massive Hydra instead
And remember: this is Modern, where Punishing Fire is banned specifically because it hurts little-creature decks too much, and Umezawa's Jitte is twice as punishing, no matter what the cards' names suggest
Im not married to that purity
For Burn Down the House to be lethal, we need our opponent to have four creatures (since each will take five damage, giving us a total of 20 thanks to Repercussion), while Star of Extinction only needs one creature on our opponent's side of the battlefield to close out the game with Repercussion
This is the passable backup mode on an already good card, and youll typically only be casting it when you really need to
Assassin Gauntlet is also an artifact, so its nicely tutorable, easy to recur, and blinkable