Apple - Lightweight Audio Waveform Viewer
It's not a Quick Look plugin, but Sound Studio it is fairly lightweight, and displays the waveform:
However, I'm afraid I don't think you'll find the waveform itself to be particularly useful for determining duplicate songs.
Try Audacity. It doesn't seem to heavyweight for just waveform viewing.
I have tried two options:
https://github.com/seagirl/QLWaveForm/releases/tag/v1.0 << that worked
https://github.com/ideoforms/qlspectrogram << Doesn't work on catalina