I'd agree with this also.
I looked at some pictures of ANH Vader from the film and the box as a whole does look larger than the MMS279 box and more the size of the R1 box, but the dials on the R1 box are undersized as you mentioned and consequently, make them look a bit too spaced out. While the dials on the MMS279 look to be the correct size, they look like they're slightly too crammed because of the smaller box. However, to my eye, the MMS279 box looks to be the more accurate one of the two because the dials don't look as crammed as much as the dials on the R1 box look spaced out.
Of course though like you said, it's one step forward and two steps backward. The size and color of the gadgets on the MMS279 box on the size of the R1 box would make for the perfect ANH chest box.