I have to agree with you, Doc...the "piano modes" on all arrangers are very lacking if you try to play as a piano player.
Haven't tried the Korg, but my experience with Yamaha and Roland arrangers was not at all satisfactory.
The user has to adjust their technique to suit the instrument which may or may not be what they want.
Ian
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Yamaha Tyros4, Yamaha MS-60S Powered Monitors(2), Yamaha CS-01, Yamaha TQ-5, Yamaha PSR-S775.