>>10907772I think they're doing it to help keep the proportions of the combined mode under control. Like Scavenger and Scrapper are both similarly sized vehicles, but Scrapper is an entire leg whereas Scavenger would normally just be an upper arm. Distributing some of Scavenger's mass down the entire arm would help even things out so as to prevent Devy from looking like he's wearing WH40K shoulder pads.
I'm not bothered by the fake treads and I think the idea is good, the only problem I have is that the forearm cover just isn't covering enough at all. I don't think it would have been much more difficult to cover the entire elbow joint properly, or at least cover more of it than this.