And I agree with you. The main reason why Schubert's piano sonatas were not popular in the 19th Century is because they were not considered to be that good, especially in regard to Beethoven's. People thought that Schubert's works were defective and that he didn't know what he was doing on account of his apparently idiosyncratic pace, use of many repetitions, and his long and drawn out landscapes especially in the last movements.@hiltroll
I know what I'm saying..
Of course, with hindsight, Schubert knew exactly what he was doing, but it wasn't until famous pianists like Schnabel, Fischer, Gilels, Serkin, Curzon, Haskill, Kempff, Brendel and others championed his works that these long-standing prejudices began to break down. Thereafter, Schubert's piano composition skills became steadily more accepted, until today he is considered to be among the best composers in this genre.
I now prefer Schubert's piano solo work to most others, including Beethoven. They may possibly be rather less technically polished than some of Beethoven's, but that's of small value to me compared with the extra depth, poetry, and feeling in Schubert's sonatas. They suit my temperament and provide more of what I want out of classical music, and are a tonic to listen to.