Only one lineage?

[Aiwendil]

I see no indication that Dior was counted mortal, some will argue that he was

Some will indeed.

Being of three races (as he indeed was) does not necessarily say anything about the matter of his mortality or immortality. He is mortal for two independent reasons: first, because he was the son of two mortals (as Luthien had indeed become mortal), and second because all those with any human blood are mortal unless specifically granted a choice. The idea of this special grace did not even exist until after Earendil reached Aman, so it certainly was not extended to Dior.