Cannabis is insidious.
Alcoholics and heroin addicts have a far better grasp, as tenuous as it may be, on how their usage is effecting them. Cannabis enthusiasts in my experience have a great tendency to count their usage as all good while discounting anything negative to other causes.
I make the concession that overall cannabis is the most socially benign drug that is readily available to most people, but I know people who are treating anxiety and depression with cannabis when the observation of everybody else in their life is that cannabis contributes to their problems rather than helps. Many people I know are having life diminishing results from cannabis but still calling it a powerful panacea. Obviously I'm speaking from bias based on my experiences. When stuff is illegal and somewhat stigmatized accurate statistical data becomes unattainable.
Cannabis: truly great for some people but a true and essentially blind downfall for many others. When exalted as a universal panacea for everyone and everything someone please call bullshit.
Answer, yes weed often causes substantial changes in personality. Sometimes for the good, sometimes very much not for the good.