Nit-picky about the necessity? Two countries were invaded without posing any threat to the US!
"Pearl Harbor may have forced our hand more clearly, so to speak, but both attacks were deep provocations."
What exactly was 9/11 a provocation to do? Most of the people involved were already dead, and they weren't state actors - they were private citizens. What exactly was that a provocation for the US to do?
"each represented a physical challenge to the United States' influence over particular spheres."
One represented a challenge to physically and economically dominate the Pacific for the foreseeable future. One represented a challenge to the structural integrity of some buildings in New York. The scale, effect and consequences are so fantastically different that I genuinely struggle to understand how they can be seen in principle as the same thing.
"But if you want to define "Pearl Harbors" as serious, potentially dangerous attacks against the US"
By this definition, 9/11, which was not a serious, potentially dangerous attack against the US, was not a Pearl Harbour. It was a criminal act that killed a lot of people and caused a lot of damage. It was not a serious threat to the US.