This thread goes off in so many directions, I thought I would not quote the many good points that were made and just add my own two cents.
My brief history: 50 years on accordion, 35 years playing arranger keyboards, 30 years playing piano, 20 years disc jockey and Karaoke artist.
I loved the accordion and still do. It's a creative instrument that allows you to emotionalize. When I switched to arranger boards, I thought it was the cat's meow at the time. Then the piano came into the picture and I really enjoyed the versatility of this magnificent instrument. Next was disc jockey time where I was working sometimes 5-6 days a week. Point being for those 4 hours on every gig, I was subconsciously listening to all kinds of music and the incredible arrangements of the songs. That gave me another whole perspective on music production. Leading up to, I'm back to playing the piano instead of my PA3x. Why? As someone already mentioned......an arranger keyboard is too robotic. And to make it NOT "too robotic" is not worth the time and energy I'd have to put into it. On the piano, I can express myself in any way I want. I don't have to concern myself with "what button for what variation....what style" 'cause I can make my own variation and styles. Same with "fills," base lines, etc.
Don't get me wrong, I still love arrangers, but my preference is now a basic piano. No gadgets, frills, bells & whistles to distract me. All my concentration can now go into creativity instead of dealing with the rigidity of working all those tabs and sliders and touch screens.
Now for my opinion on arranger players. The last good one I saw that I considered a genuine one-man-band was somewhere back in the 70's. Haven't seen one since that I like (well, I like to hear Don M play). All you hear now are vocalists who play chords behind themselves. Never approach playing a melody probably because they don't know how to. The rest are just doing the job....nothing but "robotic playing." Every song sounds the same. Very few drum breaks, no improvising on any of the 10,000 instruments in most modern arrangers, no thinking out arrangements, no modulation wheel or pitch wheel used, etc. When I was playing one of my favorite things to do was play a trombone patch melody in my left hand overriding or working against a trumpet patch melody line in my right hand in Dixieland tunes and still keeping the proper chording.
As for the giants like Marco Parisi, and the various company demonstrators.....I see them as good musicians but not great. They're good at what they do, but it all sounds the same because they all found their niche in the world of music...one set style of playing. You'll never hear Marco play a great Strauss waltz, or the Beer Barrel polka...it just ain't gonna happen. All these "greats" play "great" because they play ONE style all the time.
Now look at Billy Joel's compositions, or Elton John or the Beatles. Those are examples of musician's musicians. Billy Joel....that beautiful love song "Just the way you are" to a rocker like "My Life" to a Latin beat (Don't Ask Me Why)....complete versatility. The same with Elton John.....he goes from one style to another. The Beatles....450 songs and everyone different in structure (Yesterday, Ob-la-di, Ob-la-da, Paperback Rider).
Of all the arranger demos I've listened to in the last few years, nothing really reached out and touched me. The players were fine in many of them, but to me, a real musician can go comfortably from one genre to another and make every one sound like the real thing.
Arrangers are great, great instruments if you milk them for all they're worth. Unfortunately, in today's "instant gratification" world, players just shoot for their 15 minutes of fame on Youtube and couldn't care less about the image they're giving of an arranger keyboard. And that is why they sound "robotic" and unappealing in many ways. Nobody actually plays them like they're meant to be played.
Keep in mind that I grew up in a different era of arrangers. It was a time when more players pressed more buttons, stepped on more pedals and did their best to NOT sound "robotic!"
Mark