This is exactly what it is about. I welcome the move from Apple. Web devs can store state server side. They cry because tracking will be harder now.
Please read the HTML/Web Storage standard [0] and try to find where Apple is not honouring it.
Even before this move by Apple, you should already had to consider localStorage to be subjected to being wiped by actors not in your control.
On top of that, localStorage privacy concerns were also in the standard. See section 11.4.1 [1].
Nevertheless, I reckon Webkit should expose the option to the user.
I feel your pain, I really do, but I can't see how Apple made PWAs impossible.
[0] https://html.spec.whatwg.org/multipage/webstorage.html#webst... [1] https://html.spec.whatwg.org/multipage/webstorage.html#priva...