To be unclear about it you’d need to also have observations of people that had CTS with Dvorak but not with QWERTY. (However, it’s also clear that QWERTY is enough for some people, and that you’re likely in that category.)

Incorrect. As QWERTY is the standard, most people who have no problem with QWERTY don't switch.

Therefore, people for whom QWERTY is more efficient than Dvorak are highly unlikely to ever use Dvorak enough to develop problems (such as CTS). If, say, 10% of the population was better off with Dvorak and 90% was better off with QWERTY, you still wouldn't expect to see people developing CTS with Dvorak, then going to QWERTY, because most people start with QWERTY.

I'm not saying that QWERTY is better for anyone than Dvorak (personally the only reason I stopped using Dvorak was because I couldn't work out how to change the commands for ctrl-c, ctrl-x, ctrl-z, ctrl-s etc. to be in the same positions, rather than spread all over the keyboard) merely that it's a perfectly reasonable possibility given the evidence presented.