In Book V, Homer: The Iliad, I found that Diomedes does embody arête, which means “becoming the best you can be” or “reaching your highest human potential.” I found several instances in the book relating to the way he fought, which I felt referred to this particular saying, arête.
In Book V: Pandarus wounds Diomedes, they speak of him and how he belonged to no army, “Greek or Trojan, yet he stormed over the plain like a raging winter torrent” which I felt meant that even though he wasn’t fighting for a certain group, he had a reason to fight, and by that alone it would make him unstoppable. Diomedes was met by many who wanted to kill him, and in his path left few alive or uninjured. Again, Diomedes in this section of the book, after being injured, took his place at the front, eager to fight again, as his courage was even more intense, and went forward to attack the Trojans.
Arête also comes to mind with Diomedes in the section of the book, the death of Pandarus. Sthenelus, the son of noble Capaneus warned Diomedes of two strong warriors that were coming to fight him. Again, not wavering in his bravery, he stated, “Don’t talk to me of flight, that won’t deter me. It is not in my blood to cower away and shirk the fight: my strength’s as great as ever. I’ll not mount the chariot, but face them on foot, as I am.” This shows Diomedes as being the best he can be, reaching that highest of human potential in his efforts to fight whomever, at any cost, regardless of their strength or weapons.
Again, Diomedes represents having the strength to reach that level most men could not, or would not. In Apollo intervenes on the battlefield, he again eager to kill Aeneas, leaps at him over and over, striking him four times before slightly giving way after Apollo tells him to not think of himself as an equal to the gods. What I took this as meaning was he was getting in farther than he should, most likely succumbing to his death, because of his seemingly foolish ways in his attacks.
Overall, I feel that yes, Diomedes does embody arête, being the best he can be under the circumstances one is afforded in their lives. He was a great warrior, determined to be the finest of the Argives as Pallas Athene intended, giving him strength and courage to prove himself of this.