I think that you must realize that theory is only a tool to understand
how music is put together.  For composers that were intuitive in their
style, theory may not have been necessary for them to learn.  but,
classical music has always had a theoretical underpinning, so I doubt that
most wellknown composers had absolutely no theory training.  But, for the
aspiring composer or performer, theory can unlock some secrets of music's
construction and development that would otherwise be difficult to crack.
You could try in veign to figure out how inversion works in a Bach cannon
by trying to pinpoint melodic shapes that might inverse one another, but it
would be easier if you knew the rules of inversion and could then observe
the music and see how it outlines those rules.  Moreover, I think the way
most theory is taught today is downright borning.  It would put anyone to
sleep.  Less emphasis is placed on the ultimate aims of music theory than
is placed on the process of analysis.  To me, once you lose sight of the
ultimate purpose of understanding theory and focus exclusively on the mere
process of analyzing pieces, you lose the rue power of theory analysis.
The only reason you should need to take piece apart is to learn how to
perform it better, listen to it more deeply or to use certain compositional
processes in yoru own work.  If the analysis doesn't bring about any of
these results, it's misguided.

Orlando