I think pets should hit epic as soon as all their ability stats become maxed out, such as strength, intellegence, power, and so on. This means low level pets would reach epic fairly fast and high level pets such as sea dragons would be able to shave off around 400 training points as that is about the time my sea dragons have maxed everything out.
I mean, for a worthless pet like a Stray Piggle or Dragon that have low pedigrees and weak stats/talents people shouldn't have to spend just as much effort to level them as say, a Sea Dragon.
True - to the extent there is not much incentive to train low-Pedigree pets to Epic.
I feel sorry for all the newcomers and younger players who are taking these cheap pets to the Pavilion and putting so much time into them. They won't get a lot out of them either :P Depends on the goals of the player. Some players may like the appearance of the common pets more... For instance, I would rather have a Firecat with Sea Dragon Talents than the actual Sea Dragon.
They are also helpful for cheap Hatches when trying to help people Hatch rare pets. I can help people get can Ice Hound quite cheaply with my P-30 Ice Hound.