What made the scene epic was that it
was a clean hit that just steamrolled Doffy. The way the finale is set up is that both Luffy and Doffy are in the same state: they can barely move and only have enough energy for one attack and Luffy has claimed that he will finish the fight with a single punch. Doffy claims that taking the fight to the sky is a mistake because that's his domain and then he puts up a shield that supposedly nothing could get through considering how strong the birdcage is. And then he sends a powerful attack at Luffy through the shield. Luffy punches through the attack and the shield and sends Doffy flying through the ground into the underground port.
The scene is a call back to Luffy fighting Crocodile in Alabasta. In fact Dresrosa is a parallel to Alabasta where Crocodile was trying to become king of a country from the shadows while Doffy was king of a country out in the open. In his final clash with Crocodile, Luffy and Crocodile are underground and Crocodile attacks Luffy from above while Luffy flies up from below. Croc sends out thread blades of sand and Luffy punches through the blades, destroying them instantly, and then sends Crocodile flying up through solid bedrock with a flurry of punches, destroying part of the town, and shooting him into the sky. In his final clash with Doffy, Luffy and Doffy are in the sky and Doffy attacks from below with thread blades of string and Luffy sends a single punch down, plowing through the blades and Doffy's shield, destroying them instantly, and sending him flying down through solid ground into the underground. It's symbolic of Croc being sent up from the shadows to be exposed in the light and Doffy being cast down from heaven.