In my experience, the biggest thing that holds TIE/Ds back is high PS burst offense. With control and high damage over time, they can usually win the an extended slugfest against higher PS ships, while leveraging the Barrel Roll and PS kills to get it done against low PS beef.
It's the high PS heavy damage lists that have traditionally caused the most problems, because they cut right through AGI 3 and they take away most counterplay from the Defender. That has been intermittently popular lately, and is a traditional feature of Dengar.