What frustrating practices? I'm a developer (and mathematician), and I love puzzles :)

Not everyone is working on awesome stuff at an intelligence agency. They still need people to work on their 20 year old hellscape of an ERP system in hated language(java,ada,cobol, etc).

sure, but how much of the actual job will be solving puzzles? Seems unlikely to be representative of the work so the people who enjoy the actual work might begrudge the interview and the people who enjoy the interview might not enjoy the work.

At an intelligence agency? Possibly quite a bit.

A valid stance. Incidentally, that's why I've never had any interest in working at a certain couple of FAANG companies.