Bulkhead's biggest problem is his everything but the head. He doesn't have anywhere near the right proportions, a randomly different type of altmode, completely different kibble placement and straight-up Optimus detailing on the torso that doesn't even try to evoke either Bulkhead. Even a straight up Prime head wouldn't be as noticeable in Bulkhead's case since his face is so consumed by his mouthguard/lower jaw and the relatively simple shapes as compared to the rest of the cast.
Metroplex shows they can pull it off near-perfectly if they wanted to. Arcee, Bulkhead and Knockout are clearly just repaint fodder which would be okay if the line wasn't marketed to have emphasis on non-G1 characters pre-release.