He looks to be well bred, from what we might call heritage stock. Most folks are used to looking at hatchery birds, which by way of comparison, are much, much smaller. We have the Frank Reese (Good Shepherd) line of Barred Rocks and they are incredibly large fowl.
As for the feed. It isn't ideal to feed a rooster a constant diet of layer with the high calcium. It can impact his fertility. When feeding a mixed flock, it is preferred to feed a product everyone can eat. Give the layers their calcium on the side, as in oyster shell, rather than being ground into the feed.