To my way of thinking, an "arranger" is style pattern transformation based on real-time chord recognition. Maybe the definition includes RH harmony, or even vocal harmony driven from those same recognized chords.

If this is true, why can't Roland or ANY manufacturer put all of this in a "black box" (aka module) which could be connected via MIDI to ANY tone and effect generator: VSTs, a Ketron SD1000, or a Roland MC-80EX? Sure, more nuanced ROM samples are great. But the core arranger functionality hasn't changed much since the RA-800 of 1996.