If you saw his thread with proposed stats for the TIE defender, you would understand why he thinks it's a "Must Have." If you have a single ship that could take down any Rebel list by itself, it has to be a must include.
I am biased against this ship though. I think it looks a little gary stu-pid. But what do I know? I'm an old school fan of the originals who likes both the EU and even the prequels, even though I understand their very huge flaws.
I used to administrate for the SW Freeform RPG back in the day, and it seemed like every new player would include "Ace TIE Defender Pilot" if they were playing Imperial. I don't have anything against them, and for the sake of filling out the game, I would certainly love to see them. What I don't want is a ship as powerful as that one can be. I'm amazed they didn't cram a Turbolaser Cannon into it's stats somehow.
I never really cared for the Defender, myself. In that particular run of new TIE types, the Avenger was always my favorite. If you go through ALL TIE types that have been put forth by any legitimate publication, it's a tie (no pun intended) between the Avenger and the Interceptor, followed closely by the x1.