i think alot of the suggesting issues is with the collaborative filtering model often used in suggesting songs in a streaming music service.
The collaborative filtering model is not well suited for communities with extremely high variance within a specific genre. In other words, in the context of the model, classical, and classical sub genres are not differentiated enough, in terms of individual interest, to form a new independent cluster. The example being, I like romantic era classical, but i don't thumbs down at the first note of a classical/period classical piece. It's that openness that retrospectively is killing the model.
A human curated classical playlists like on 8track, I suspect produces a better experience (of course depending on who put the list together). Crowd sourcing beats collaborative filtering here it seems.
Your 100% correct saying centuries of music all labeled as classical is the first problem, BUT I would say the sub-genres are fairly strong. Your example for Romantic period is almost 100 years of music from 1820 to World War I.
Jazz streaming is much better but that has a very much shorter music period and clearer sub-genres.
THE PROBLEM: Live Classical is amazing and recorded Classical is meh. Same thing with Gospel music, most Jazz and Opera. If you have never heard a 75+ Gospel Choir live you really are missing an awesome experience and same can be said of Blues.
Most modern music sounds the same or MUCH BETTER recorded. Think EDM, pop music (That is the reason why most performances are more karaoke ie No back up band or even better no band and lip syncing).
