My reasons for using an arranger are very different from your "pro" reasons.

I always liked music. But for various reasons that really don't belong here, (read laziness) I never had the patience and never dedicated the time required to learn to "properly" (eg read notes) play music on any instrument. Thank God I have a good ear.

The first arranger I saw was a Panasonic (if I remember well), model unknown, around 1983. The disovery that this thing could play accompaniments was a revelation.

Next was a Yamaha PSS or early PSR, with about 15 different rhythms, and PCM drums, around 1987.

In 1991, one of the teachers in my vocational college was an "on the side" musician. A denture maker in the day, a musician in the night. Classically trained, (classical singer), he had a superb voice and a Technics KN-600 or something that blew me away. the sound and the realism was better than anything I had ever heard.

2-3 years later I got my Casio.

Why an arranger? For me, it is simply an easy way to play what I like, without having to learn to move my left hand much. 3 finger chords are OK and sometimes I can manage a 7th or two. The right hand plays a recognizable melody and that's it, I am having a good time. I may describe the arranger as the venerable "musical crutch" but that's what it is for me, and I am thankful they were invented. Better to have a wooden leg than no leg at all, right?