When I'm playing a game of Demigod and one particular player keeps killing me over and over, I eventually learn that that particular player is to be feared. I play more conservatively around them than I would around, say, an AI: I don't chase them into towers as much, I don't fight them if I'm injured / low on mana; in extreme cases (where someone has bought a few artifacts, say) I just flee as soon as I see them.
The AI doesn't do this. If I've been able to buy enough items to kill it quickly over and over, it should not just keep running up to me to be killed again (thus giving me more gold and making its position even worse). It should stay out of range, stay near safety, grab flags / attack structures that I'm far away from, try to attack the weaker members of my team instead, come after me in groups, etc. Even if the AI still loses, this would give it much more of a feeling that you're playing an opponent who adapts to circumstances, not just a predictable automaton.