Site logo display is low quality
After a lot of trial and error, I realised that as long as the image goes through processing by Drupal, it's resolution somehow deteriorates during the process. As the issue with the site logo was a client complaint, I chose to bypass Drupal processing altogether by replacing site logo with site title, then applying text-indent: -9999px and background: url("../logo-image.png") to render the logo instead.