Yeah I understand that, I'm trying to dig each concept slowly and thoroughly now, but the difficulty with those classics is that they often use lots of modulations, modal interchange, chord inversions, Neapolitan chords, nonharmonic tones, weird chord progressions, cadences, etc, which is a pain both to read, interpret and understand what's going on in the music sheet! There's also the problem that too much music theory often leads to analysis paralysis so we often need to practice balancing that which is challenging as well!
Thanks for the reference tho!