your point being that most any pianist can learn those works, to merely coordinate those notes and play those pieces isnt as much of a technical challenge as , say, playing 10/2 in just over a minute.
then yes, in an atheletic way, that is true, but those pieces arent necesarily atheletically any less challenging than the others, and maybe even moreso - if played at a 'competitive' tempo.
alkan's music is generally very difficult, lots of different techniques involved, and especially unique in his music's difficulty is sheer endurance and keeping up a tempo during the onslaughts.
godowsky's chopin studies should UNDOUBTEDLY be included, because i completely disagree that these arent atheletically demanding, you are maybe just used to hamelin's 'lazy' recordings.
the godowsky studies are completely unique and revolutionary in their use of the left hand, they demand intense use of fingers and figurations that had never been used before.
ask a pianist to play - the LH 10/2 10/4 and 10/12, as rapidly as possible and with utmost control, and you will have a complete assesment of their left hand technical capibilities, except maybe sustained octaves(which can be assessed in other repertoire..)
things like islamey and alkan's 39/10 are very difficult all-round technique tests, and especially good for assesing raw endurance of the player's complete mechanism, if played at a 'competitive' tempo
