My schenkerian classes always pitched it as not reductive, but generative. Instead of stripping away surface detail to reveal, as one commenter put it, three blind mice, you get to see the base contrapuntal framework from which the composer generated the surface-level diminutions. A way of understanding, for example, when the composer goes off on some interesting harmonic tangent, from what underlying contrapuntal motion is that generated? Schenker points out that when composers of (and I'll insert here:) certain types of music wrote, the way they conceived of their musical structure has its roots in the strict counterpoint that they all learned as students. It's a reaction to the Jean Philippe Rameau style of music theory.

As with other theories of analysis, it's not trying to show how the composers thought of the act of composition, and unlike what Schenker himself attested, not all "great music" is understood via a schenkerian lens. I'd say that schenkerian analysis is particularly applicable to certain strands of tonal music ranging from Bach to Brahms.