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This is what drove me to uninstall Facebook, twitter, etc. I use their websites if I occasionally want to visit. I don't want notifications hooking me into my phone.

You're right - the app sandbox model in iOS prevents inter-app communication of notifications, and there is no iOS equivalent to the Android ListenerNotificationService API.

For me the biggest pain was email.

I created a free and open source set of filters to fix this. Soooo much better.

https://unfuck.email

This addresses email notifications only. There is a lot of apps that would send you notifications that you want to see like your hardware needs attention but also sends some useless promo notifications