Apart from the typical opposing team pets being 1-2 levels higher than your highest pet. The system is also matching pets that are most commonly rare pets AND pets that are better matched against the ones you are using.
If you also take a look at the actual player you are going agaist, 95% of the time they are completely decked out in the most perfect and straight forward 'Tier Gear'. Somehow I don't think random players you go against will always be pure Tier gear and look stock standard for it.
I would dare say we are not playing against another 'player', more so we are playing against a bot, which through the pvp pet battle system is ultimately making it unfair against the team you choose to play with, as stated above.
What the concern here is not all of us have the time to run around each leveling area just to try and get a wild pet to battle against and constantly have to keep waiting for 8mins at a time to heal the pets you are using to continue on.
The game does have other things you/me/anyone would like to do, e.g. Questing, Dungeons, Raids, Farming, Profession leveling etc. etc. So how does it make it fair that you have to lose 90% of the time due to Blizzards unfair PvP pet battle system and then be told "go and level your pet(s) with the wild ones" ??
Honestly, come on?