How does one remove the loudness graph that is overlaid on the progress bar in Plexamp for IOS?
You cannot hide that graph.
As for „that is overlaid…“: it looks like the waveform/loudness graph is used as the actual progress bar 
You are correct. It is the actual progress bar. Is there anyway I can get a standard bar as a progress bar like other music players have? The loudness graph is something I don’t care for and it ruins the otherwise beautiful aesthetics of the app.
No, you can’t.