Hello people. Am not sure whether you will agree with me 100% that the grading system is inaccurate.According to the system Chopins waltze op.64.No2 is only grade 7, whereas his Fantasie Impromptu is grade 8.
Are you talking about the ABRSM Grading system where Grade 8 is the highest level before the Associate levels? I'm not that familiar with it but I would guess that these pieces would be placed at that relative level. I think Fantasie Impromptu is a much more difficult piece than the Waltz.
The RCM (Royal Conservatory of Music -Toronto) syllabus puts the Impromptu at the ARCT (Associate) level and the Waltz in Grade 9. (RCM have 10 grades before the Associate level.)
Beethovens sonata op.27 No2 is only grade 7 whereas Chopins Etude op.25,No1 is grade 8.
Are you talking about the first movement of Sonata 27/2? I would say that the level would be below the 25/1 Etude.
RCM has the entire Sonata at the ARCT level. All the Op.25 Etudes with the exception of No.2 are listed at this level as well.
Well for some reason it took me 2 years to learn the waltze but only three days for the fantasie impromptu.
It took me much longer to learn the Impromptu than the Waltz and I have never learned any piece in recent memory in mere days. I'm a slow learner. (In more ways than one1)

In my humble oppinion the Beethoven sonata is far more demanding than the Chopin Etude,since it has taken me 10 years to learn the sonata and only a few months for the Etude. Please give me your oppinion on this subject.I mean what are they looking at the music or the fingers.
I'm presently working on the 2nd and 3rd movements of the Sonata and they are challenging. I would agree that the Sonata seems to be more demanding than the Etude, although I don't play the Etude.
Cheers
allthumbs