I think Virgil purposely portrays Aeneas less than a hero. May be Virgil really didnt think much of Ceaser Augustus' achievements and the imperial Rome, when considering the individual loss involved in it. Thus, through Aeneus' character Virgil is trying to say that when you weigh the imperial gains and the personal losses, the losses outweighs the imperial glory. Thus, Augustus (whom Aeneas portrays for the most part) with all his imperial power gained nothing.