I guess that explains why the Empire went with the TIE Interceptor instead of the TIE Defender as their secondary fighter, since they were already tooled for mass-producing maneuverable fighters that were meant to fight with numerical advantage. If their existing strategy worked against everything besides X-wings, Thrawn's full-throated advocacy of the TIE/d would start to look less like foresightedness and more like reinventing the wheel.
Yup.
Think of it this way.
"What's better, one well rounded fighter than can do anything you want it to, or four stripped down ones that can reliably
kill that one well rounded uberfighter when used appropriately. Even if a couple of ours die, we're not actually spending more than you are"
The problem here is that the the Empire couldn't cross that conceptual gap of "Just because we
can throw four fighters to your every one
doesn't mean we'll always have that kind of numerical superiority", because they couldn't get out of the mindset that wars and conflicts ultimately boil down to big setpiece battles where you can expect to bring everything you need to the table in order to win. In short, their planning was for 'The war they expected to fight', and not what it actually turned out to be--which is to say, a galactic scale counterinsurgency against a foe with its own heavy industry and shipbuilding. They assumed they'd always be on the offense with the forces they'd want--and the Rebellion just refused to give them that fight until the Battle of Endor.
And wouldn't you know it? Even putting the DS2 out of consideration, the Rebellion
was getting its ass handed to it there. The Empire built to force decisive battles and
win them by weight of its superior industry. Even the Death Stars fit that doctrine! By presenting a target that
must be engaged, they effectively had the ability to force the Rebellion to stand and fight where the Empire was strong, instead of where they were weak.
So TIE Interceptors were the logical extension of that, as they were only marginally more expensive and doubled down on the TIE Fighter's strengths as seen by the admirality. Meanwhile, the TIE Defender was... 'Literally why? It costs a fortune and the performance increase doesn't warrant the price hike'
Even though the TIE Defender was a
natural counter to the X-Wing, and putting a wing of those together as a rapid response element would have severely curtained the Rebellion's capacity to hit and run locations of its choosing. In terms of the set piece battles that the Empire was built to force and win? They were only a marginal gain for vastly increased cost.
