How do you mention you can play multiple audio streams at the same time and then claim the OS is designed to let only one app access an audio channel / device? Which one is it now? Let's dig a bit deeper into this:

Also, let's not blame everything on the OS vendor being malicious. In most cases, playing multiple audio streams simultaneously would be annoying. In android, you can absolutely play multiple sources simultaneously, and Android will mix everything together and play it.

That being said, starting with API level 31, Android actually started to enforce a concept called audio focus at the system level. That would be around Android version 12. Audio focus is basically a token that can be requested and handed from app to app, and only the app holding the token gets to talk, everything else is faded out.

I'll agree that enforcing this and not making it configurable for the end user was a pretty dumb move, but that was simply a UX decision, not certainly malicious.

If your phone is rooted, you can work around it, e. g. via an xposed module.