As a user, let me give you an entirely different viewpoint. I love Jack, and see no alternative, for this:
I can have different applications send audio output to different devices.
Almost all applications want to send audio to the default audio device. (Which makes sense, right?). So, with Jack, and no programs being jack-aware other than QJackCtl, I can tell all these different programs which device to use.
If you can name any alternative to this, please do. I am on a Mac.