I don't work in airport security.
My family emigrated from the UK to Australia in 1968 when I was 5yo. We made three trips back to the UK in 1969, 1971 and 1973.
In 1968, I can remember that security was essentially non-existent; in the early 1970s, certainly by 1973
hijackings had become a regular phenomenon and security such as metal detectors had been introduced. Over time the character of threats changed, from hijackings, taking an aircraft and those on board hostage to make political demands, during the 1970s, to efforts to destroy aircraft in flight, eg:
Lockerbie.
While suicide attacks had occurred before, what changed with 9/11 was the recognition that the hijacked aircraft itself could be used as a weapon to cause far more death and destruction that just one plane and its passengers. Suddenly the stakes were far higher.
Has security since 2001 been effective? By and large, yes - but your task is to find evidence. Wikipedia isn't evidence, but it can often lead you to more reliable sources. Have a look at how the frequency, character, and locations of hijackings has changed over the years from the late 60s to the present in the list at my first link. Remember too that there is no end to change, no final perfect security solution. Threats become more sophisticated, so responses must also continue to evolve. For example
in 2006 major changes affecting carrying liquids on board were introduced in response to new threats.
You might also like to look into the success of the Israelis in preventing hijackings and bombings on El Al, both before and after 2001; they use a much more sophisticated and targeted approach to security than the blunt "security theatre" seen elsewhere.
Without writing your essay for you, hopefully this has given you some ideas to think about.