From the FAQ at https://colemak.com/FAQ#What.27s_wrong_ … _layout.3F
The main problem with Dvorak is that it's too difficult and frustrating to learn for existing QWERTY typists because it's so different from QWERTY. Colemak has been designed to be easy to learn.
The biggest difficulty is in getting anyone to consider a change of layout, not what form the layout is. Almost half - 16 of 33 - keys change position when moving from Sholes to Colemak. I personally do not see this as a big advantage over the Dvorak, even though this changes the positions of all but two keys (A and M). A layout is a gestalt, and has to be learned as a whole.
Dr. Dvorak designed his Simplified Layout to be 'easier to learn' too - and it is.
Placing 'L' on the QWERTY 'P' position causes excessive strain on the right pinky. Colemak doesn't place frequent letters where the pinkies stretch.
The 'Dactylograph' at https://infohost.nmt.edu/~shipman/ergo/parkinson.html clearly shows that using the Sholes layout, the right pinky is under-utilized: it does only 1.7% (!) of the work. The Dvorak layout corrects this imbalance, sharing out finger loads more evenly and in proportion to their strengths.
Anyone moving from Sholes to Dvorak will go from not having to use that right pinky very much at all, to having to use it quite a bit more. Naturally this will feel as though this digit is being 'overworked,' but the truth is that it hasn't been carrying its fair share of the load up to then!
It is significantly lopsided so that the right hand does too much work.
Again referring to the 'Dactylograph,' using Dvorak the (intentional) split is 45.7% left, 54.3% right. Referring to this as being 'significantly lopsided' is an exaggeration. For comparison, what is the split on the Colemak? It cannot be totally 50-50!
It's not comfortable to use Ctrl-Z/X/C/V shortcuts with the left hand while holding the mouse with the right hand. Colemak conserves those shortcuts in their QWERTY positions.
Whilst this is a fair observation, Ctrl-Z/X/C/V are not the only options for these common functions. E.g. consider, respectively, Alt+Backspace/Shift+Delete/Ctrl+Insert/Shift+Insert, though I grant you that these will also be hard to use if a main criterium is consideration of a (right-handed) rodent. Nor are these the only keyboard shortcuts - there are many others that have to be re-learnt as a result of switching to a different layout.
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There are trillions of possible keyboard layouts, probably a great many of these could be argued as being 'the best' for various reasons.
The fact that so many people who are clearly pro-change have chosen to promote yet another alternative layout reminds me of the Popular Front of Judea (Life of Brian).
"We should be struggling together!"
"We are!"