Quite frankly I think you have it completely backwards--most Arfs are lighter than most of us build! I am not saying that someone using contest grade wood wouldn't do better, but I will argue that compared to typical kit wood, the Arfs come out pretty respectable. At least one factor is that they are plastic covered (for better or worse!).
I remember my ARF Nobler coming in around 40oz or so with a Brodak 40. I don't recall the exact number, but my review of it which appeared in Stunt News gave the weight. This review was copied from the original (but now lost) SSW Review section. I remember reading it in Stunt News and wondering why it sounded familiar!