I don't think we are in a similar position. All being aircraft debris, it is not only consistent with the story that an aircraft crashed there but, coupled with further physical evidence, radar data and witness statements, it is evidence of the fact. The only problem I see is that the presence of debris and this other evidence does not conclude specific identity of the aircraft.
You are talking fantasy: “one small piece” and “selective ejection”? There was debris scattered all over the place inside the building and across the lawn. Lots of it, all over. There was fuselage and landing gear and wheels and engine components. It’s right there in the pictures I’ve linked you before and which are freely available online. The fuselage debris ejected backwards at the Pentagon impact and explosion exactly as it did at the WTC which can be seen in video footage. There is no difference in the physics involved. The backward ejection of debris is completely expected: -