"What do bands really want from a keyboard player?"

LOL someone that melds with the music thats there and enhances it. Someone that adds dynamics...and on and on. I think the potential role of a keyboard player in a full band has been demonstrated millions of times. Not really some big mystery.

"It is good to be able to play by yourself - you do not depend on other musicians"

Yeah you just depend on prefab styles, midi, and a device

"I would suggest that the next improvement the arrangers can introduce is the controlled variability of style parts "

Why not just sequence your own backing tracks from scratch, seems like that would solve the "in the can" issue...unless your the type that waits for Yamaha ( or others ) to make more "in the can" styles with some form of calculated diversity.

"they have the skill to keep up with the arranger accompaniment tracks."

Sorry...its not a matter of skill, any musician worth half his salt can run circles around auto accompaniment. If the musician is familiar with the song has a good ear for improv and on and on.