Whoever it is NOT easier than all of the paganini etudes . I think you seriously underestimate the difficulty. (I say this respectfully). The 4th paganini etude is a walk in the park compared to un sospiro. I also think the 1st paganini etude is much easier. 5th is debatably more or less difficult, but only half the paganini etudes 2, 3, and 6 are undoubtedly all harder. Btw the 4th paganini etude is the easiest etude liszt ever composed. Un sospiro is musically extremely challenging also. I'd say its the second hardest concert etude behind la leggierezza. Its also harder than transcendental etudes 1, 2 and 3.
Difficulty can be a subjective thing though. I think gnomenreigen has tricky things to deal with too.
That is one hundred percent true. As per whether gnomenreigen is more difficult is subjective. However what is not subjective is that un sospiro is far tougher than paganini etude 4.