While I have not upgraded my 6S Plus because it has the headphone jack, it is hard to make a water tight device when the users keep asking for holes to be put into the case.
Besides, it’s not an excuse. Samsung can design a waterproof phone with headphone jack. Why can’t Apple?
As much I as a musician, who can't stand the unplayable latency of bluetooth headphones with any of my daily drivers, such as Garageband, and has invested in extremely high-quality headphones with cables, would take the headphone jack over a waterproof phone in a heartbeat; I have to say [citation needed]...
That's a bold statement to make. While I'd prefer a headphone jack, due to my particular use case, most of my friends have or have no problem with using wireless headphones, and many of them have also lost phones or other electronics to even a small amount of water in the wrong place.
Obviously this just anecdata but let me tell you that wireless headphones/earbuds have not even been a consideration for most people. Heck, even first world countries have lots of people still using wired earbuds for most use cases.
I heard lots of grumbling about the loss of headphone jacks. I never even once heard someone say "this is not waterproof? I won't buy it!"