Why diluted, because hebis not the product of an incest, like others? Well he is not the first Targaryen, if that it is what you mean.
The type of marriage has caused issue in the background stories. In the case of the Dance of Dragon, the first civil war, and bastard rebellions. If Danny and Vis, if he had lived, were married their offspring could have a stronger claim due to maintaining tradition. However Vis is dead so marriage traditions regarding incest are moot. Beside Jon is still a bastard as Rhaegar's lawful wife was a Martell. If Don and Danny marry the point is moot as he could be King anyways. There was blatantly obvious in scenes which attempted to imply that this is possible. Danny gives up her lover for a
chance at a political marriage followed by Jon being shown as a Targy. He is now Stark and Targy now which bring the North into the fold while maintain tradition as close as possible. Although this seems far too overt for what I expect from Martin.