I think the real issue isn't with pet classes, but with T8-strength pets available to any lvl 70. Any other class as a fresh 70 can scarcely sustain the T8 spells/discs because they don't have enough mana/endurance for it with the low gear. Give a fresh lvl 70 a T8 pet spell and they only have to cast it once - easily sustainable near-T8 dps for a fresh 70 pet class.
I think that's the only real issue here, because T8 pets aren't that great once you're in Tier 8. With mega buffs and donor gear they become 'good', in my experience, but not 'great'. I encourage anyone that is unsure to simply parse their toon or have their guildies parse theirs. It's not as amazing as some would have you believe.
If this is a big enough issue to do something about, then here are the options as I see them, in no particular order:
[1] Make some/all future dropped/bought T8 spells NO TRADE. Or just a select few (like the 1k godly point ones). All existing T8 spells that are un-memmed and tradable could remain so until they're memmed. They'll disappear soon enough over time.
[2] Nerf pets, balancing the early tiers and unbalancing the later tiers.
[3] Nerf pets, boost pet owners.
[4] Make T8 pet power scale with progression flags, where the final T8 flag allows 100% pet power for the Rk. I pets, T7 flag allows 80% pet power and so on...