The overwhelming majority of agents I have encountered have been polite, but according to a number of GAO studies, they aren't particularly effective either as individuals tasked with spotting dangerous items or as an organization giving the agents the tools and systems they need to be effective. In 2017, they had a failure rate of 95%. Then a new sheriff came to town, got the test results classified, and then said they had dramatically improved.
The agents are tested and they routinely fail to find things like guns in baggage. AI could be very helpful here as it never gets tired or bored.
The whole showing your boarding pass and matching it to an ID can be easily circumvented. Have someone buy a ticket who isn't on the no fly list, print a fake boarding pass at home with your real name, show your id and fake boarding pass to TSA, fly with the other person's ticket. Its child's play but the reason it hasn't been fixed in 25 years is that it doesn't matter.
Its a joke. Its been a joke for 2 decades. It hasn't caught a single terrorist that we know of, and surely TSA would trumpet any success. It costs $10B a year and our civil liberties to make people feel like they are safer.