The vase from Vulci is an important piece of evidence that Aeneas was of interest in central Italy before the Romans appropriated his story. It is also enlightening that the artist or patron chose to depict this. It is more common in the surviving corpus to find Aeneas carrying his father Anchises away from Troy, rather than his brief fight with Diomedes.
This depiction is also important because it suggests that the story was internalized in Etruscan (or at least Vulcentine) culture. As Otto Brendel pointed out some time ago, its “painter […] was well conversant with Greek art, which, however, he translated into a personal idiom of noticeably Etruscan flavor.”Show O. J. Brendel, Etruscan Art (1995), p. 198.
In particular, I think that the arms are more in-line with contemporary Etruscan art found elsewhere, notably Diomedes’ sword and shield and the mixed presence of archers and spearmen. The device on Diomedes’ shield is striking and rather odd.
That the depiction was not copied directly from a known Greek example is telling. It suggests that this part of Aeneas’ story was one of the elements of the Trojan myth that found a home in Italy.