Good posts guys. Chas is just a rich old man too, but makes some good points.
Spalding kept me from writing exactly what I was thinking!
One thought though (of course), it's easy to assume that arranger players started as piano players and are using it for a substitute. That's not true in many cases. I started as a trumpet player, found there was not much market for those, even though I was really good (he says modestly). So I got a bass and started playing for parties after about a week. Learned enough guitar to know I wasn't ever going to be James Burton, bought an organ because my band back home needed an organ player.
Started doing singles because they paid more. Graduated through several organs as the auto-accomp. got better and better. Along about here I quit my "real" job.
THEN I discovered there was a world outside of organs, dollies, leslies and big vans to haul them in. Arrangers were invented.
Thank you Lord, for that, because I haven't had to work hard since!
To make the point, I'm an ARRANGER player, not a piano player. I don't like piano keys, I don't play left-hand arpeggios, I'm lousy at the sustain pedal. But I can sit down and entertain an audience for four hours, several nights a week, and never play the same song twice!
Yes the arranger does the background, but if you play with a band, the band does the background. Without me telling it what to do, the arranger just sets there. If you want it to do something great, you must tell it the right chords, put in the right riffs, put in variations, breaks, fill-ins for variety, play the right rides--that's where the PLAYING comes in.
Also, it doesn't bother me if another old man sits down and plays three-chord songs with one finger. He can't get my job, but he can sure have fun "playing".
Also, I've heard bad singers trying to use pitch correction, and they still sounded bad. Not saying you can't do it in a high-end studio or even with the right computer program, but I've never heard it done on the bandstand.
I TOLD you I didn't have much to add.