I'm probably not the etude-genious in this club
However, as a liszt-chopin fan like everyone else, I would say Op10no2 by Chopin is not at all difficult compared to other etudes
In example the 'thirds' etude. I don't know about everyone else, but this is something I really suck at, so that might be why...
Else would I say that op10no4 is more difficult than no2. But mind that Chopin in itself often is butter compared to Liszt(purely technically). Chopins technique-difficult pieces(Revolutionary, Winterwind) which also can be seen in the ballads,scherzos, walzes, etc, is usually based upon motorique skills which can easily be trained. Liszt is not that way. He always makes you cry for rehearsing something you did'nt need more than two bars on 11 pages...
Liszts 12 etudes trancendante is not easy loaf. Look at nr2. And then at Mazeppa, and Wilde Jagd. And Nr10. These pieces are not played by man. I believe they are written for those one step above on the food chain...