People have somehow managed to forget this, but phones have been waterproof since ... basically forever without forgoing a headphone jack. I could link probably half the phones made between 2012-2017, but this phone is actually linked by the site itself: https://www.theverge.com/2015/10/16/9549247/sony-xperia-z5-r...
Honestly, I'm not sure what the issue is supposed to be here. I've literally never, in 12 years of owning a smartphone, dropped it in water. I have no clue how that's even supposed to happen short of it falling into a river.
Since this is a small phone, I suspect most people will probably not be using a case that adds significantly to the size. Just a guess on my part though. I can live with a camera bump if I have to, I just think a lot of us miss the candy bar designs of ~2014-2015.