I'm no expert on tonewheel organ sounds. But I have a decent ear for sound and like most people I've heard the real thing. In my opinion the XW-P1's clonewheel organ would be okay in a mix. Just not as a lead instrument, unless you restrict yourself to a subset of possible B3 sounds and avoid the rotary effect and the overdrive. According to Mike Martin of Casio you can improve the "bare" (i.e. non-rotary, non-overdrive) drawbar sound by adjusting the XW-P1's master equalizer, which I have yet to try.
Of course, attach a Ventilator and its another story (I don't have one). But then, from what I've heard a Ventilator can make almost any clonewheel sound more authentic.