You have asked a loaded question. The ones calling Haydn easy are stupid poo poo ignoramus heads.
We must keep in mind the norms of the times at which they were composed. The sonata was not normally for performance by the top musicians or the public stage, they were for the most part for amateurs and the evening entertainment in home's drawing rooms, parlors, salons. The concerto was the realm of the virtuosos of the day for the most part.
Haydn's vast sonata output is all over the place partly for this reason. Many composers of the time composed the sonatas for their students (or themselves ). The "all over the place " difficulty range of Haydn sonatas attests the the varied abilities of his students and dedicatees.
However there was some music that was composed for the touring professional stage performer. This wonderful sonata ( my favorite of his ) is one of those. It also hilights and takes advantage of the regions more advanced piano of the time with its wide range ( uses the highest note of any or almost any of the sonatas if I recall ).
This lovely lady gets it. And has the technical and musical chops to really make this piece shine. It is one of his most difficult sonatas. I love it. Will probably learn it myself, I just bought the Henle volume iii of the collected works which contains this one.
Hugz, kiss. -Alee Marie
