First off, for those attempting to draw a distinction between “offensive” and “defensive” weapons, such a distinction is essentially spurious. IF it helps you sleep better at night, good on ya, but it’s a fantasy. Now, there IS purely defensive EQUIPMENT, such as body armor and the like, but again, as those who attempt to ban possession of body armor by civilians recognize, having better defensive equipment allows one to be more effective on offense.
Second, the military has a huge need for “design”. Human factor consideration is massive in military “stuff”. “Form follows function.” Engineers focus on making it work, and then making it fit into whatever space. Lots of opportunities for designers to bring their skill, including their aesthetic skills, but because of the “engineer culture” infusing the defense, it’s likely a bit rougher of a ride than in other fields.