I just went over and cranked up the Genos to check out using the joystick with those JS organ sounds. IMHO, fail. The joystick doesn't really do a Leslie tone cabinet emulation at all, from slow speed to fast speed. The joystick is still acting as an on/off switch for a tremolo effect, with the only change taking place is the amplitude of the tremolo effect. Matter of fact, you can see the "rotary" button light just above it light up when the tremolo amplitude has reached a certain point. There is no apparent change in rotational effect speed of the "rotary" speaker nature of the Leslie tone cabinets whatsoever. I listened to this very closely. My wife happened to be over in that room with me at the time, and I was showing her the difference. Her only comment was that the effect produced by the JS organ voices just sounded awful. And she is not a keyboard player.
And honestly, even if the joystick operation did produce a true rotary speaker/Leslie effect, IMHO, it would be pretty much useless on an arranger keyboard used as an arranger. Not unless you were using chord loops for your playing, because you just wouldn't have enough hands to effect chord changes in the accompaniment, play the lead melody, and slowly push up on the joystick to emulate the ramping up in speed and slowing down of same of that organ voice.
As for the switch used with my Hammond B3 and the Leslie tone cabinets, I used the standard lever type toggle switch mounted just below the base note keys on the lower keyboard, activated with my left palm in a sweeping motion, until I found I had that "three hand" problem more often than not, and eventually converted it over to a foot switch, which worked a WHOLE lot better in actual playing. Even using the joystick if you wanted to have analog control over the depth of the tremolo, you would still have that "three hand" problem to deal with. So what was the point?
So from the evidence I see, there is no way to actually use those JS organ voices to produce a true (or even just mostly) satisfactory Leslie tone cabinet emulation. I still stand by my claim this is an error on Yamaha's part mostly from the evidence that the JS organ voice with "Whiter" in the title of it, clearly indicating it's target emulation is for the song "Whiter Shade of Pale". And it would fail completely in that regard since anyone familiar with the song would NOT use if for that purpose at all. Again, IMHO.
IMHO, I would prefer just deleting them if they cannot be fixed to work properly.
I pointed Yamaha to this thread and am still awaiting a response from them