As someone who gets marketing calls every fine day, I agree with your every word. And with gp too.

The problem with not implementing notifications is that when they are useful (instant dispatch software), they are not implemented. But honestly I’d just spin up a telegram or email bot, if clients were not brainwashed with tekhnology. Messages and email are notifications. It is also a matter of minutes, opposed to creating a stupid service worker client-server-like runtime and trying to get things right without any test mode (long story short, implementing and debugging webpush requires publishing every change to a certified https host). There is even an entire company that sells you a properly configured webpush as a service. That’s just stupid.

Odd argument. SMS is a hellscape to DIY (especially financially), email even more so with DKIM. If by SMS/email you mean "Twilio" or "Mailchimp," well, that's no different than using a third party push service.