See, I think a Dark Mark for Draco, being the sign of the *highest* honour, would not gel with how he was characterised in DH. I could see him Marked pre-DH, but not post. I think that if Draco were given the honour of being inducted into Voldemort's inner circle, he would have been breaking his back to do right by Voldemort because of his family's tenuous position, seizing this opportunity to prove himself. But he just wasn't trying all that hard; some would argue that he even worked to undermine Voldemort's plans when he "failed to recognise" Harry at Malfoy Manor (that scene can be read in more than one way, though).

Fandom essays are not at all like academic essays, in my experience (this was very distressing when I was new >_>); you're pretty much guaranteed to see a pet theory stated as hard fact. I've seen people say, post-DH, that Lucius is too!1 an abusive parent and that Snape is alive!1 as part of a broader discussion of canon, so go figure.