We had hundreds of hijackings in the 20th century, culminating in 9/11, the first time an airplane was used as a weapon of mass destruction. Since 9/11, following the subsequent addition of TSA and stronger protocols, we haven't had any more hijackings.
25 years of success would suggest that TSA, or at least the enhanced security protocols that included TSA, combined with better focused intelligence, has worked to eliminate the threat of hijacking, more or less.