There are hundreds and hundreds of MIDI (NOT Super Midi) styles available in PG catalogue. There is a "way" to extract a specific instrumental line from individual style, but the way it is done is not intuitive at all.

I feel that huge chunk of content (thousands and thousands of instrumental stems) is simply lost to most of users including myself, because of awkward way these are "selected".

Kindly consider a normal way of auditioning + selecting MIDI stems from PG MIDI styles.
SAME way we would select Real tracks... or even Super Midi tracks.