"Good enough for Samsung" is very, very low bar.

It could have been removed too because app developers didn't use it, because they couldn't make it stable or because they couldn't make it work together with mic permissions.

Anyway, I'm interested in numbers, and specifically whether switching from Android Audio or OpenSL to AAudio brings any significant improvement.

What the hell is Android Audio?

I suggest you to educate yourself in Android audio subsytems.

It's a name that's sometimes used for AudioTrack, AudioRecord and related classes under android.media. Does that collection have an official name? I would also suggest that you learn some manners.

Well, as someone with Android development experience I never saw it mentioned like that anywhere.

I guess this means you don't have any idea about the actual latency difference. It's okay to not know things, you don't have to be a jerk about it.