Originally, I didn't think heroic victories would work with the ai. I thought, naturally, that the autoresolve for ai/ai battles made the best army win. The crossed swords disprove this now that I think about it.
Anyhow, many moons ago I made some traits to count and record up to 150 (overkill!) major victories individually ( all battles vs greater odds) and was happy to see an ai general with 2 of these under his belt. Are battleodds just numbers of troops rather than army strength?
When I saw this rare ai general I thought it would be a good idea to get these guys to hang around even longer and so my other idea that I'd like to suggest is for victorious ai generals to get maximum healing after battles so these great armies don't just dwindle away by their 2nd battle. "oh no, not him again" you may remark as you are repeatedly defeated by the same guy. I think this adds to the excitement.
I add a value of 70 healing in with the ai stars traits (new troops flocking to fill the ranks of a successful general, perhaps). I use this ,but don't actually know if this value is limited. It may not work, but in Rome at least, you could get values at least up to 25 through combined traits.