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."
The resting curl of your hand is important, as is relative finger lengths (particularly of the pinky).
And then there's resting thumb position relative to the fingers.