yup, round shape is the preferred shape.
and they can be nearly circular in shape. slant or slope head, pointed or beaked mouth are generally not preferred.
flo is correct the problem is more common in discus at your LFS ..the best shaped discus are found with discus breeders..
often large breeders will sell the b, c quality fish to fish stores keeping the A or prime fish for them selves or their customers.
the stunting occurs , as mentioned, when the fish arrives at the LFS.where they usually don't have the time or resources to care properly for the juveniles.
again, nice color and with good care this discus will provide you with many years(yes they live a long time) of enjoyment.
btw when I first ventured into discus I settled for B quality as this was more affordable for me to partake in the adventure.
I now purchase the A quality ..which even given proper care you may find a lower quality discus in the mix.
I purchase them in groups of 6