Because the journey to Epic on a pet is time consuming and fairly boring, I'd like to suggest that pets get BATTLE EXPERIENCE points as well as points when you train using the games.
I would give it 1 point per level of creature being battled, each time it battles. It would still be pretty slow, but at least it could get a small boost towards a level that way. Would still have to play the games to get anywhere, just would be a nice little boost.
Also, it would be nice to make it so the better abilities show up at ancient and epic with no chance of a dud talent (for example, like mana or spirited) at epic. No one wants to work that hard, and be that bored, to get a nothing talent at epic. I'd rather discard a bad pet right away and start on a new one than get burned at epic.
That being said, I enjoy the pets but think it could be a lot more fun, with more reward for the effort than it is presently. If anyone else has a suggestion, please post.
I like this idea, but maybe just 1 xp for every 2 or 3 ranks? Otherwise, people could just level grind their pets in Celestia, where many enemies are Rank 9 through 11.