Why are notifications on iOS such a nightmare? It’s impossible to properly read just a selection or to quickly dismiss many at once.

Because neither the shareholders or the userbase cares about this. Apple has a captive market who accepted this limitation for over 10 years and thee won't switch to Android because of that issue.

Entification will only continue from here on both parties since they've achieved duopoly status, so as a customer you can only pick the lesser of two evils.