> They're very rare in pre-romantic classical music...
Not true. Some styles of classical music employ dissonance in a prominent way - from late 14th century Ars Subtilior, through the pre-baroque stylus fantasticus and the bold chromaticism of Gesualdo, Frescobaldi, de Macke and others, and to the late baroque with Bach, Vivaldi, Zelenka, Rebel and others.