ReplayGain is nice - but note it doesn’t ’fix the compression’. Compression and dynamic range is about loud/quiet _within_ the track. ReplayGain just turns the volume up and down for the entire track, the point being so all your tracks play back at about the same level. It saves a preset on the volume knob for you essentially.

If you remember making a playlist where one song is suddenly much louder than the last, and you’re riding the volume knob on every other song, you’ll see why this is nice!