There's no one-size-fits-all ergo keyboard, which is why the dactyl has a configurator.
This is a bit of a trope in places like /r/ErgoMechKeyboards/. However, it's a bit of an empty statement without further data. Of course hand sizes/shapes differ, but the question is if they differ enough to preclude designs that work for a majority of the population. If you look at e.g. hand length/width datasets, within a group (e.g. men) these are close to a normal distribution. And the spread is not that large. e.g. the different in hand width in the ANSUR II 2012 dataset is 0.6cm between the 25th and the 75th percentile for men. The difference in hand length is 1.3 cm between the 25th and 75th percentile.
So, it's very likely to be possible to design a keyboard that fits most people well enough. Sure, if your hand size is an outlier you may have to get creative.
Besides that, there is also some latitude in designing ergo keyboards for multiple hand sizes. See eg. how Moergo iterated for several years so come up with a design that works for many different hand sizes [1].
Hand sizes differ a lot, and finger mobility does too. Also, the length of the ring finger is different for different people. So yeah, there's a definite requirement for different keyboards for different people. And it's not a "meme" or a trope, it does make a huge difference. Plus, it depends on the layout you use (or are hoping to build) and the work that you do with your keyboard, and the kinds of features you're using (tap dance, macros, expansion, combos, etc) and how many of them you can remember. Sure, you can go with a bog-standard split and it'll be MUCH better than a regular QWERTY. But if your needs dictate a better keyboard, it doesn't mean you're hyperoptimizing.
The same applies to all these dimensions. They are not completely random and most will be normally distributed when measured. Also, as I said keyboards can accommodate multiple lenghts e.g. by having multiple thumb keys where you use a subset of them.
At any rate, I have seen plenty of folks who had issues like wrist pains, etc. that were resolved by improving posture, taking regular breaks, doing exercises and switching to a split, tented keyboard (just a boring one with a traditional layout like a Freestyle).
Only people who went (too?) far down the rabbit hole do all these micro-optimizations and proclaim that their keyboard is 'the end game' after having used it for a few weeks. Until the next end game :).
"Even more surprising, when Daniels averaged all his data, the average hand did not resemble any individual’s measurements. There was no such thing as an average hand size."
This is a bit of a trope in places like /r/ErgoMechKeyboards/. However, it's a bit of an empty statement without further data. Of course hand sizes/shapes differ, but the question is if they differ enough to preclude designs that work for a majority of the population. If you look at e.g. hand length/width datasets, within a group (e.g. men) these are close to a normal distribution. And the spread is not that large. e.g. the different in hand width in the ANSUR II 2012 dataset is 0.6cm between the 25th and the 75th percentile for men. The difference in hand length is 1.3 cm between the 25th and 75th percentile.
So, it's very likely to be possible to design a keyboard that fits most people well enough. Sure, if your hand size is an outlier you may have to get creative.
Besides that, there is also some latitude in designing ergo keyboards for multiple hand sizes. See eg. how Moergo iterated for several years so come up with a design that works for many different hand sizes [1].
[1] https://www.moergo.com/pages/glove80-ergonomic-keyboard-desi...