Sadly the developer will play dumb and Apple will do nothing about it. Seen that, been there, nothing has changed ever. The only recourse is to disable notifications for that particular app.

I have emailed a developer in the past and they apologized and as far as I remember, I haven't had that issue since then. So I think it depends upon each developer.

For small apps it is possible I guess. Problem is that many large companies use this practice. I've tried to reason with The Fork and the French rail company to no avail for example. They know they don't risk anything by violating this rule and Apple has no high ground as they violate this same rule themselves.

That's fair. The one I emailed was a solo developer I believe. I think if enough people make noise about it (make a post on such apps abusing the system on /r/apple) and then send it to Apple, they will take action.