I think the more accurate way to conceptualise this is that treatment works by interfering with processes in the brain that cause depression, not that it cancel

I think the more accurate way to conceptualise this is that treatment works by interfering with processes in the brain that cause depression, not that it cancels out the depression by adding enough euphoria/mania/happyness to compensate. Antidepressants don't typically cause mania in healthy people, but they could paradoxically cause depression.