You can't compare the two because any argument that says "weed is bad because it causes severe mental health problems" or "alcohol is bad because it causes severe rage, depression etc." is assuming that a person is taking enough of the substance to cause any damage at all. You could take both in moderation and see no effects whatsoever.
The quantity matters a lot. You could only ask the question "Is 5 beers worse than 2 spliffs" and name the beers and marijuana you're using, then you can answer based on scientific evidence.
The reason weed is banned is because it causes immediate psychological effects from small amounts + the point of smoking weed is to get high whilst the point of drinking is not always to get drunk. It can also be really addictive and be the centre of a person's life. Alcohol does not have severe immediate effects and alcohol has a way of preventing people overdosing on it (passing out, throwing up).
Thus I can conclude to you that neither is worse than the other, but marijuana should be banned and alcohol not because of the nature of a human being which is to overdose on good things.
Hope you agree,