Hi Dennis,
amazing how far BIAB has come. I'd been updating biab every couple of years or so, since about 1990 ?? when it first came out for the Atari. Only thing I ever used it for was to to convert the odd BIAB style across to my current keyboard of the day. Lets face it , the biab songs never sounded as good as a song on an arranger.
Then about 3 or 4 years ago, I bought a new more powerful laptop, so I decided to try the realtracks which I'd been discarding, because my old laptop hadn't been capable of running them properly. Wow, I was amazed, and they've only been getting better.
I think the fact that backing can't be played in realtime puts a lot of arranger keyboard players off. Basically what a great way of putting together a backing track , though.
Also the styles are different. Heavily into country, rock & jazz. Some of those guitar real tracks sound amazing.

A while back, I was fiddling round with doing a mix of arranger tracks mixed with BIAB tracks for a song ie record the backing track using the korg, and replacing the guitar tracks in the song with realtracks from biab. Even as good as some of the guitar mode tracks are in the PA3X, the Realtracks in BIAB sound better ( or , at least to me).
It was an interesting way of making an older converted style sound better. Some of the guitar tracks in early styles were pretty awful, especially when converted across to another keyboard.
Ok, so one has to sacrifice realtime style playing, but what's wrong with a backing track to play or sing along to.

Shouldn't really be a case of either /or, arrangers & biab compliment each other very well.