As you know they are different and not easily comparable. Alcohol leaves the body quickly, but THC is oil soluble and remains in fat cells for quite a long time. So it is not just a matter of dosage.
As to which is more wrong, that depends on how they affect the user.
That said, both should be absolute verboten for young people.
When it's in fat cells it's not attaching to neuroreceptors, so has no relevance to impairment.