The biggest advantage for having a good AAC encoder isn't efficiency, it's that for nearly the past 2 decades the de facto standard for live streamed video has been RTMP with H.264 video and AAC audio. There is basically no support for any other codecs. If you want to send a video stream to Youtube or Twitch, you will be sending H.264 and AAC. If you want an idea of how ubiquitous this is, I just checked in OBS and it will not even let you select different video and audio codecs in streaming mode, it just (correctly) assumes that anybody who's streaming will be streaming H.264 and AAC.

I think the biggest issue with Opus is the problem with its specification being lacking, see:

https://nothings.org/stb/stb_opus.html

This essentially causes opus to never be used in games or in things in stores that may have issues with specific licenses.

I would like Opus, but I’m using a subsonic client on iOS and my choice has been Flac (Alac?), MP3, or AAC. Opus wouldn’t play (There are some that supported it, but I didn’t like their UX).

Choosing a lossy audio codec has become such a no brainer. Either use opus and be done with it or if for some reason opus cannot be used then use aac for compatibility with insane high bitrate for good quality without having to do research on what encoder and mode to pick.

Still having a good quality and default aac encoder is great. Though I don't get why it is mainly CBR.

> Man what a showcase for Opus this is.

I take it you mean this Opus (https://en.wikipedia.org/wiki/Opus_(audio_format)) not that Opus (https://en.wikipedia.org/wiki/Claude_(AI)).

I read almost all the way through your comment thinking there was a decent probability you were saying this new AAC encoder was written with Claude Opus.