Shifting attacks from one method to another is not necessarily useless. If what would have been the most effective method is reduced in its effectiveness, and as a result, another less effective method becomes the most effective one, and the used one, that reduces the effectiveness of attacks.
That wording was convoluted.
What I mean is,
if they would have done plane attacks because of plane attacks working best for them, then making plane attacks not work as well, and therefore making them shift to something else, means that whatever they are doing for attacks wouldn't work as well for attacks as the plane attacks would have, which is a benefit.
That's not to say that the TSA is beneficial, or that it does really reduce the effectiveness of adversaries.
I'm just saying that, assuming that it is true that adversaries shift their attacks from air travel to other methods as a result of the TSA , that would suggest that adversaries are restricted by the TSA , and made somewhat less effective (assuming that adversaries weren't overestimating the effectiveness of air travel attacks originally).