It may be a pozidriv, but I guarantee you the vast majority are being removed and installed with a #2 phillips driver, chalk it up to government efficiency again, lol. However, as egregious of a fastener sin as this is, to my knowledge it has yet to cause a catastrophic incident or frequent work stoppages.

The slotteds are maybe a step up from a thumb screw, not much torque at all on those, If you have to use an impact driver someone fucked up intentionally in such a way that it would almost constitute deliberate sabotage. They're recessed below the panel so you need a little something for purchase, hence the slot. They're also integral to the component, so no chance of FOD with those.

It's a 50 year old airframe, torx was still relatively new around the same time it was first being drawn up. Torq-set has been around since the late 50's or early 60's IIRC and is a proven NASM standard. They went with what they knew worked in an aviation application, and it gets the job done well enough. And, as I was pointing out in my last comment, it's typically one kind of fastener per job, unless its a fairly big job. So the work flows fairly smoothly considering the age of the aircraft and number of subcontractors involved.