In the context of 9/11, that seems like a strong statement to make.
The terrorists (let us agree on this label a priori) got everything they could ever wish for and then some.
Regular Americans in general lost freedoms of movement and communication. The whole political landscape shifted right. The US invaded and destabilized Iraq and Afghanistan. Pakistan and Syria got weaker than ever. The Saudis gained hugely in influence over the whole region.
Wahhabism is now influential in areas where they hardly existed before! They almost controlled Egypt for a while. And when the US retreated and gave controlling power back to the Taliban they showed the whole world that a needle pick in the belly of the beast was all that was necessary. That has given new courage to similar terrorist cells, a situation the rest of the world is still struggling with.
The whole world focused for almost two decades on their part of the world. Nobody can say that 9/11 wasn't an important catalyst for all that. And at a price that would not even cover catering had this been an organized intelligence operation. Terrorism can clearly and empirically be a very cost effective lever in ideological, political and religious struggle.