I think that the reason arrangers don't get much respect in the US (we're a small fraction of the total keyboard market) is that there is very little development of styles in these rap and hiphop styles....... Oh yes, you'll find a few on your arranger, but outnumbered by ballroom styles 20-1, 30-1 etc..
Plus they just don't seem to have much 'flava', sort of a middle of the road version of rap.
Tritons and Motifs are FLYING off the shelves in the US, in large part due to the excellent, cutting edge arpeggiated and beat-boxed patches that sound like something phresh off the radio. Try one in the store, you think that you could be a rap star........... Try an arranger, you think you're going to play an old folks home!
BUT.......... there is no technical reason why any of the top-of-the-line arrangers can't make the same beats, but no-one programs them that way! The voicing team that makes the slammin' beats in a FantomX never gets used by Roland to make styles for the G70, etc..
If any of these companies chose to address the needs of the younger (at heart!) generation, rather than their corporate roadmaps, Tyros2's and G70s would be all the rage in the 'hood and their bottom lines would soar!
Because of the simple repetitive nature of modern urban music, arrangers are BY FAR the best tool to make it with (at least live......), and only need better, younger style programmers, and perhaps an SRX board with more urban drumkits and sounds on it (more profit!!) to dominate the workstation market.
After all, just like most other forms of music, it's easier and more fun to do it on an arranger than have to program it on a workstation.........
_________________________
An arranger is just a tool. What matters is what you build with it..!