I would love to see a double-blind RSI study where they randomly assigned different people different keyboards with different amounts of travel, etc.

I think it's fair to say that typing style can be worse than the keyboard, but I also suspect that a keyboard where you "never have to even lift your fingers" causes more RSI than one that requires more activity.

Why do you suspect that?

Less activity means weaker muscles, and our muscles evolved for a wide range of movements. Reduced movement is generally less healthy in the long run, but feels easier in the short run.