Try a route from T3 (I hear Cape Town is lovely when it's not having a drought) and you'll find that (in my opinion) it is specifically T5 security that is dour, borderline aggressive, and extremely slow at any exception handling. The staff in T5 act like they've both got a huge chip on their shoulder and are in a bitter work-to-rule-and-go-slow-too workplace dispute - except the First Wing at T5, which is lovely and almost up to Japanese standards.
So no, I don't think it's just you.