Sounds like a reasonable compromise!
Not really. Heroic victories aren't really that common, in my experience. Discounting defensive sieges (which I think should be excluded out of fairness to the AI), this trait if triggered only by field battles would have a marginal affect. It would, however, be great for roleplaying with national heroes much like having your own Hannibal or Scipio and serve as an incentive to the player to act a bit more daringly than he would otherwise (which would definitely fit with historical reality of Roman aristocrats competing for glory).
Besides, a +3 command and +3 morale boost doesn't exactly make your commander into some uber overlord immortal god emperor crushing everything in his path and your generals don't live forever, dying off after age 72. I never amass more than about 20 to 30 field battles as heroic victories in an entire campaign, and I play very long 800-1000 turn campaigns into the late 1st century BC. I think you guys are just exaggerating the affect this would have and overlooking how awesomely cool it would be.