American Bulldog is every bit the mastiff the bullmastiff is. They used mastiff type dogs to get the American Bulldog's size. Depends on how technical you want to get with it. Molosser is a much more ancient word....and dog type than "mastiff". Many dogs can fall into the mastiff classification....even Dogo's and Bullmastiffs. The bullmastiff started out trying to achieve and 60/40 cross of mastiff/bulldog. I believe that shifted more towards the bulldog for them. Anatolians and Kangals, and even the shepherd dogs from the Caucasus Mts can be classified as molossers, yet not mastiffs, which both terms are used pretty loosely nowadays....especially mastiff. If you can call a Dogue, Bullmastiff and a Dogo mastiff, then I say yes. I'm not a fan of bulldogs at all but compared to mastiffs, the American Bulldog is employed as it was intended more than any of these other mastiffs. I would even have to say that it's not a molosser, but a modern day mastiff.