This is only one component of the optimization though. Eg. letter frequency will be different. For instance, the relative frequency of "z" is about 4.9% in Poli

This is only one component of the optimization though. Eg. letter frequency will be different. For instance, the relative frequency of "z" is about 4.9% in Polish, whereas as low as 0.07% in English (according to https://en.wikipedia.org/wiki/Letter_frequency https://en.wikipedia.org/wiki/Letter_frequency). The same goes for what the most popular 2-grams and 3-grams are, and conversely, the calculated stroke path (or how much do the typist's fingers have to 'travel', independently of the hand alternation rate), the use of the weakest fingers enforced by a given layout, etc. This likely doesn't nullify all the benefits of Dvorak, or some other English-optimized layouts - but it certainly reduces them, while the adoption cost is still the same.