I think it is always important to account for the millions of people worldwide who arent as technologically savy as some folks out there. It is a hard thing to wrap our heads around with since we are in this day and age were tech is improving so quickly, but some people just cant deal with having to remember to charge it, pair it, etc.
Personally, I too think the wireless is the way to go, especially if bluetooth 5.0 earphones starts to come out in masses, but for now, I also believe that it doesnt hurt to keep the headphone jack in place.
I look at it this way, if the phone is gonna cost the same, why not have an extra feature in there in case I actually need to use it? Or rather, why take it away if there is no other improvements? I am coming from a samsung line of phones and having a headphone jack taken away but having nothing in there wouldnt be cool. At this point, the phones stopped going for slimmer phones so they arent gonna get slimmer as well, so taking the headphone jack away as a reason to have the phone slimmer is a bs reason imo. The only reason I see them (as in samsung) removing it is if they put dual speakers in there. When Apple did it, I believe it was a bit too soon, but now that bluetooth 5.0 is inside the phone and the wireless earphone businesses slowly adapting to the change, I believe the next year's phone might remove it.
I also personally do not care much about dual speakers or mono speakers because I simply do not even rely on the speaker grills on the phone itself. That is just me though, I cant recall myself using my phone and needing quality sound to be coming out of my phone speakers.
Some companies like LG are adding drivers on their phone to allow for better audio experience and thats cool too.
So basically to sum it up, Im basically saying that the phones now are slim enough..so to remove the headphone jack for thar reason, it is bs...there should be something universally better should replace it, and not something that is controversial or 50-50.