Anything other than peer demos is a case of damned if you do, damned if you don't.
Mind you, I am surprised that some absolutely terrible user demos somehow don't get used as 'proof' that the instrument sucks in the first place, but a bad demo by some flack at NAMM that probably only saw the thing for the first time that day is offered up as proof incontrovertible.
Someone does an amazing launch demo, and people go 'That's sequenced, and massaged' (I remember seeing several Tyros 2 factory demos that, while being different players, was essentially the same performance with minor variations), and someone does a bad demo and it's all of a sudden the arranger's problem.
I have heard amazing factory demos for the T4 and Audya both, but OTOH, I have yet to hear a user demo that came close. Put these great keyboards in the hands of mere mortals, and you are going to get average (or less!) results.
Thank God, IMO it's still 90% the player. Then 10% preparation. And, in fairness, with BOTH, almost any arranger can be made to sound wonderful. And with them missing, any arranger can be made to sound BAD!
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An arranger is just a tool. What matters is what you build with it..!