The following is pure speculation from my own observation:
I suspect the T8 dummy has ludicrously high AC. Higher than any raid boss I've encountered. Melee players consistently do very low dmg against this dummy. If my observations ring any truth, then the T8 dummy is far from an accurate representation of class balancing.
The pets, in particular, would stand out in this scenario (and they do) because they have vastly more ATTK than players. ATTK that high can overcome absurdly high AC, and thus pets do the same dmg vs the T8 dummy as they do against any boss.
As for your int casters... your wizards are doing shockingly low dmg. Non-donor with full raid buffs/debuffs, I can get a consistent 40-45k dps from mine against a dummy. Maybe your wiz didn't have enchanter buffs & bard songs.
A good time to revive viewtopic.php?f=30&t=9882 ! I haven't updated what I do on that post in quite some time.