I liked Addison too. Before the 2nd round started, I really wanted Akil Thomas (underage offensive C), Addison (underage offensive RHD), or Durzi (overage two-way D). I was happy to get one of them.
BUT the issue with your argument is this: You DON'T draft based on if you have spots on your AHL roster, that's just silly. You draft based on BPA. If Dubas liked Durzi as the BPA, then there's zero issue.
Put yourself in a Leafs management's shoes in 2017-2018. Your NHL D-core is not great, you have Dermott developing, you just drafted Lilijegren the year before, and you just drafted Sandin in the 1st round. Your AHL D-core doesn't look good (Didn't have Rosen/Borgman/Sandin/Lilijegren on the AHL team then), you have no idea what it'll look like. Do you honestly skip out on your BPA because you think there's going to be no room on the AHL lineup when he's 20 years old???