Assuming equal gear, it's not BS. There's this thing called damage, and then there're interrupts and CC, 6 DPS vs. 4 heals, if the DPS have more than half a brain it's very doable. Not to mention Sorc heals don't even require interrupts anymore.
No one would build a premade with 4, or really even more than 1, so I have no clue where you pulled that from.