I really don't think people who type slowly do so because of QWERTY. Anecdotally, my dad basically isn't able to develop muscle memory for the key locations and will frequently revert to the "scan and then press with one finger" method. You could give him any layout and he would still type slowly. Pretty sure even an alphabetical order would trip him up, because it'd need to be broken into multiple rows, so he'd need muscle memory again.
And while this is speculative, given how close typing speeds seem on a cursory search between layouts, this suggests to me that the vast majority of the performance comes not from the layout, but from touch typing and effective use of multiple hands and fingers at the same time. All layout agnostic skills.
This is not to say that on an input method level, things cannot be further improved. I sometimes see stenography [0] related software and demonstrations on YouTube for example. It also isn't to say that there cannot be a benefit health wise (i.e. ergonomically) to alternative layouts. It's just that for speed I'm not convinced it affects much, and so I think it's the wrong thing to try and change. Especially considering that sometimes things that are suboptimal can be better by being the standard.
I would agree with something like that, that e.g. it's only useful when you have a set text ready that you want typed in.
Personally I clock in around 110 wpm at my fastest (in English), and I'll only reach that in practice when I have intense disagreements with people over the internet (colleagues, friends or randoms). Outside of that, it's barely useful.
Stenographers have special keyboards that type phrases, not keys, so their speed is also extremely fast due to only a subset of character combinations needed.
And while this is speculative, given how close typing speeds seem on a cursory search between layouts, this suggests to me that the vast majority of the performance comes not from the layout, but from touch typing and effective use of multiple hands and fingers at the same time. All layout agnostic skills.
This is not to say that on an input method level, things cannot be further improved. I sometimes see stenography [0] related software and demonstrations on YouTube for example. It also isn't to say that there cannot be a benefit health wise (i.e. ergonomically) to alternative layouts. It's just that for speed I'm not convinced it affects much, and so I think it's the wrong thing to try and change. Especially considering that sometimes things that are suboptimal can be better by being the standard.
[0] https://en.wikipedia.org/wiki/Stenotype