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 :).
