Completely agree, Bill. The skill set of a good organist is considerably higher than most arranger players, as a large amount of what is heard is actually being played, not provided by a machine!
You need good foot skills for basslines, and your LH is expected to do MUCH more than simply hold down a chord!
One thing that organs seem to provide that arrangers on the whole don't, is the ability to layer certain drum or percussion sounds with either the feet or LH sounds, often only sounding on notes you play hard. You try to do this with many arrangers, and you run into the problem that the sounds either transpose while you play if a Normal sound, or you put up a kit, and the sound you want is only available on the one note! Both are rubbish for the task in hand...
But being able to trigger a crash, or a snare accent with a strong hit allows you to vary the monotonous drum beat in a totally interactive way, tied to what you are playing. This ups the realism in a big way.
The really sad thing is, basically, most modern MOTL arrangers and up CAN do tricks like this. In other words, their underlying engines don't stop the function from being possible. They all are capable of responding on all 16 MIDI Channels, so multiple splits are no issue. They are all mostly capable of putting certain sounds on ONLY hard or soft velocity strikes, most of them can change sounds (or crossfade between two or more) by using the expression pedal, basically everything that makes a modern organ so good.
But until we ASK for these features, we are being treated as bastard stepchildren of the music world, incapable of using them! I often get the impression that arranger designers design arrangers for the WORST of us, not the best of us! I certainly don't feel that with modern organ designers...
It is such a shame that you can't add a MIDI pedal set, a second, dumb one MIDI channel keyboard, and have every feature that organists get. There's honestly no reason we can't, other than asking the designers to add the features... The underlying engines are certainly capable of it.
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An arranger is just a tool. What matters is what you build with it..!