About 45 years ago when I first began keeping and breeding wild Discus the plain looking Xingu Browns were among the most common of the wild Browns I received. They were not far from the major export centers but over the years they have been fished out to the point that they are no longer in plentiful supply.
In the States, they are not very popular because of their relative lack of blue striations and the publics' tastes now seem to lean more to the Discus which have strong red over tones on their bodies like those from the Alenquer and Nhamunda areas. I don't see that the shapes of Xingu are very different from other wild Discus. All wild Discus have better body shapes(IMO)than any of the domestic forms.
Your Xingu are still young fish which have not filled out in thickness. Discus at that stage do have a more gracile look but that will change as they fully mature.