Given how important Facebook is to so many people (plus just the sheer size of its userbase) I literally do not think it is possible for them to make any changes whatsoever that do not provoke some sort of backlash. If they merged Messenger back into the main app there would certainly be an uproar over that as well.

That's not entirely true - they forced me to uninstall the app and just use the website on my mobile browser.

Depressingly I am pretty sure it's a better UX than the app was - just without notifications.