Being a professional musician, if you allow drummers to be considered musicians, I have had to opportunity to observe many people who consume both alcohol and cannibis.
First of all I agree that cannibis is less dangerous alone than distilled alcohol is alone. To be fair though I believe that beer and wine is less dangerous than cannibis.
However, I do not agree that the personality effects are uniform. As a first approximation the cannibis effects are for most people towards depression and relaxation. But for 1/4-1/3 of the population the cannibis effects are towards mania or hyperactivity.
As far as I can tell, which direction the effects go depend on the person's personality to begin with. If you tend to be depressed, quiet, nonverbal and withdrawn the effects of cannibis are to make you elated, creative, verbal and interactive with other people.
However, if you consume enough cannibis, you will become relaxed and then depressed. Either way the effects do not seem to be permanent unless cannibis is consumed on a more than regular basis, like every day.
People, who to begin with are engaging, etc., (just the opposite of the above type) become immediately more relaxed and with enough consumption depressed. They, lets call them type A, become less ambitious while the type Bs become more ambitious and motivated by their own ideas. After sobering up they (type Bs) usually find that what they thought were creative ideas are not so. Their music does improve until consumption is so much that technique fails.
What have others on this forum with cannibis consuming friends noticed about personality changes from either alcohol or cannibis?