You might need to hatch with different pets to get some better talents in your pool, but if you think about it the odds are always worse at higher levels If you are going for a mega pet with 5 specific talents that you know are in the pool you have 5/10 at teen, 4/9 at adult, 3/8 at ancient, 2/7 at epic, but only 1/6 at mega. The closer you get to perfect, the harder it is to get.
In reality no pet fails at Mega. They failed at hatch, since all talents are set upon hatching. You could do what many players do and wait for test realm to train new pets.
wow only 6 fails at mega? I failed 81 or so times at mega making a perfect storm beetle for general game. Proof, defy, pain, fairy, current. this was just self hatching though i knew all 10 slots and what they were. I kept getting cast tower or critical striker as the annoying talents that i did not want. but even so knowing all 10 slots does help you will get that perfect pet eventually :)
need to shock the pets - doing the same two parents over and over does not always work they get really sticky.