Which would be even thicker on a thicker phone.

If the goal is strictly to minimize thickness, then it probably would've been less hassle to develop a slightly thinner case than to remove the 3.5mm jack.

Based on my experience (which is worth next to nothing), people don't really care about the thickness of their phone. Most people I know end up throwing it in a hideous Otterbox (or similarly gigantic case) anyway. Who's going to notice an extra millimeter matter then?

Yes. That's why I have one of the Cat ruggedized phones. It's thinner than some iPhones in their cases.