Yeah I agree that was deeply unsatisfying. That beating scene is one of the darkest and ugliest moments in any superhero movie, so it's frustrating that we never get to see Superman confront them again.
Having a now-fully powered Superman beat up a couple of normal crooks would have been overkill at best (and deliberate murder at worst, since a punch from him would have resulted in them having broken skulls.) The ice ledge falling down on some of the crooks and Brutus having the piano slammed into him by Jason on board the Gertrude
was a great old-fashioned 'hoist by their own petard' move right out of the old MPAA Production Code that people didn't get because they wanted action all of the time and for Superman to kill somebody (BTW, those objecting to the action in the current flick should note that this always happens in the current comic books: Superman-and the Justice League in the first story arc of the new Justice League
comic book-can't always save everybody in the nick of time, some will die.) Superman waked into a trap? He didn't know that Luthor had stolen kryptonite and used it as a base element to grow the crystal continent; even so, he did what he did because he's like that.