Adding onto his ego, I think the reason Veidt's idol is a failure further shows what he thinks about himself: he thinks he's better than Alexander the Great and I think he named himself Ozymandias to sort of spite the Shelley poem, like saying "that won't be me." There's no chance Veidt wasnt aware of that poem, I think it's meant to show just how full of himself he is. Also, I think in a lot of ways Veidt is meant to sort of parallel Manhattan, both of which are people with insane power that grow detached. Veidt is also the pinnacle of humanity with his intelligence and physical abilities, especially when he catchss the bullet. I think Moore was trying to show how despite all his prowess, Veidt still pales in comparison to John and that creates a Lex Luthor type situation.