Picture from theoi.com
Diomedes' aristeia seems to be a discussion of the role of the gods on the battlefield, in relation to individuals as well as to the whole army. The gods Ares, Aphrodite, Apollo, Hera and Athena come to the foreground while Zeus remains only a spectator. Apparently the 'plan of Zeus' of Il 2.1- still has not kicked in yet.
It is also a picture of - in what I call the Chimaera model - the lion's head of the beast.
The lion: brave, fierce king of the beasts. In the simile's it knows how to attack but also when to retreat.
Diomedes' picture is ironical, not because his learning curve is untrue or invalid, but because it asks the young listener a question: "do you really think it will be like that?"
The negative answer to that is in the pictures of Menelaos and ultimately, Achilles.