I agree that any additional number of fast jets based wherever is not going to make us considerably safer.
a) hijack an airliner by force b) do it so quickly that there's no chance, not even 5 seconds, for an RT distress call
Unfortunately safety measures tend to be reactive, based on past experiences. The next "hostile" can not be expected to do exactly the same as previous ones. Instead of going through the considerable pain of hijacking, if I was a "hostile", I'd consider leasing one of the many inexpensive older a/c, preferrably without crew...if an AOC is a problem, then with crew, and take the a/c while crew is on night stop, file a flight plan, answer radio transmissions, and don't attract any attention. Any deviations from flight plan, or non-compliance with ATC should immediately be explained.
If i was to allocate a budget to prevent such things from happening, I'd prefer better intelligence, to stop "hostiles" at an earlier point, rather than more fast jets.