Christ... how deep are they? Mine were covered in what could be described as spiderweb cracks, very tiny, but covering the entire surface of the lights. Took about 1 hour to sand each headlight back to smooth with coarse grit paper, then another couple of hours with progressively finer grade, before polishing.
I tried several polishes, but not the Meguiars, which is over 20€ here. None were that good tbh. Heard about toothpaste, gave it a go and it was perfect for the job. I did buy a polishing wheel for the drill though, as my arms were falling off by then.