There's no background sync, proper offline, no notifications, no (usable) indexeddb, no rtc, no file system, no media sinks, no media sessions ... these are from the top of my head.
You have a point that long time ago Apple was the one pushing the browser as application platform but today is not the same as the long gone past.
Edit: The can-i-use about "web audio" is misleading about Safari. The web audio is prefixed there with "webkit" is not the same as the standard API.
Edit2: Noticed it's not about "web audio" at all but html5 audio. That's an API from 2010 that doesn't really do anything for apps such as games or audio editors. The newer Web Audio API is used for this and that's what I am referring to.