One of the things that I appreciate about this mod is that they prioritized being true to the Legends canon over game balance when the two clearly conflicted. In the case of TIE Defenders, they clearly conflict, because the TIE Defenders honestly are/were that good/overpowered compared to everything else in the SW universe at the time.
A TIE Defender fleet is my attack force of last resort as the IR, as I generally find myself not needing them even on Admiral (if you strike the enemy AI early enough and hard enough, they'll never build up enough of a doom stack for you to need them), and I find it slightly more appealing to go with SSD/VSD-2/Lancer fleets over an all-fighter fleet from a canonical Imperial doctrine perspective. 40 TIE Defenders are, essentially, an automatic win for the IR, which is cool for a couple of battles before it gets boring. By the time I've had enough time to build up that fleet, though, the campaign is usually effectively over anyway, so I find it's a crutch that while available, is rarely necessary.