Secondarily, Schubert is more classified as a Romantic composer rather than a Classical/Baroque composer for a reason. Not only are his melodies and harmonies romantic (textbook definition) in nature, but what distinguishes Schubert from all other composers of his era were his unique rhythms. I play his along with Chopin's pieces as written - lots of polyrhythm. Thanks for creating this forum!
I don't know what classifies Schubert as a Romantic composer, but we can be fairly sure that it is not the fact that he notates dotted eights/sixteenths against triplets and means it.
The problem we, in our time, have here is one of convention.
Conventions die out slowly. When the first pianos were invented, harpsichords, clavichords, and virginals did not disappear. They existed for decades, while pianos grew in popularity.
So it is with notation: slowly, composers entered into a more and more precise form of notation. Less could be taken for granted as belonging to an enclosed musical culture. Bach could write, in the gigue of the B-flat partita, a whole movement of dotted eights/sixteenths vs. triplets, and it is fairly obvious what he meant.
Schubert, on the other hand, was on a cusp of a radical change. It was a new thing for composers to actually write down the way the music should sound in a
practical way.
Conventions existed in learned circles which would have dotted eighths/sixteenths and triplets even out; however practical notation (look at the impromptu in c minor) negated such a theoretical perspective.
Now, today, we are equally prisoners of convention. We think that all composers, in all epochs, notated music exactly
as it should be heard. We are sorely mistaken. It is only in modern times, that composers agreed on a conventional notation that was universal and objective. When we apply the standards of Stravinsky, Bartok, Messiaen, and Boulez to composers of two or three hundred years ago, we err grievously.
No doubt: we should always ask, was something specific and intentional meant by this notation? But we should also be prepared for the answer, "no." And that is what is sorely lacking in musicians of today: creativity. The ability to say, "no, all the parameters were not defined on a piece of paper. We have to interpret this by our own tastes."
Random thoughts.
Walter Ramsey