You know, it's been such a weird winter. A lot of infertility. A lot of die offs. Especially the silkies. I ordered 20 from Meyers. 6 Golden Comets, 7 White Rocks and 7 Delawares. The first two group are growing like gangbusters. The Delawares were puny. 1 DOA and 3 more died over the 1st week. Of the 3 left I have one that is very small (male) and two big strapping females. So I think it was just the type this year.Mine were in transit from Wed. to Fri. morning. I was at work, but DH unpacked them and dipped their beaks, etc. They had plenty of space, two waterers and two feeders. There is no competition for anything. There haven't been any losses now in two days. I picked up one each of the red and blacks, and yes - the reds are obviously heavier and like you said, shaped more like a broiler than the blacks. At 9 days old, they definitely have some weight to them. It will be interesting to see how they all turn out.
My set-up. it shows less than half of their space. They are in an 8x8 coop, and the barrier was taken down within a few days. I'd say it was at least 5' in diameter.
One the other hand, yours are smaller and look different from the reds. I think they gave you a ringer.