T/T here's a pic of what the disc looks like, note the badly spayed hub/bell lol.

OK, refresh my grey matter, these were all 2nd hand parts? What about the brake pads?
Give it 250 miles of moderate braking to properly bed in the pads, and see if it improves!
Otherwise, maybe the part of the caliper where the pad slides has a build-up of rust, or even paint, which is stopping free movement of the pads. You may need to strip them down again and properly clean the pad guides, and lubricate them with some proper v.high temp anti-sieze paste, and not the lithium based grease which VW recommends (and which goes up in smoke and fire!).