I could be completely wrong. I don't express this to assert it, but rather to ask if anyone else has noticed anything similar.
A sober individual's brain is operating on standard (often societally installed) reward mechanism, including "succeeding" on certain self-evaluated measures like "contributions to society"
It's commonly said that weed makes you "OK with being bored". i.e. standard reward mechanisms mentioned above don't really matter much when you're high.
It has nothing to do with narcissism or sense of superiority as you call it, just that their reward mechanism doesn't include things like "how much am I contributing to society". Apathy is a better word for it.
Most stoners in particular people who smoke a lot and for a long time at least in my experience become apathetic and to a degree dependent on their environment. They rely on others to organize their lives, even get simple chores done, they become sort of lethargic. And when you have an individual like that who also acts indifferently towards it you create (I think a justified) negative perception.
There is selection bias at play, as someone with an admitted negative perception of stoners you probably haven't put yourself in many situations where you might meet counterexamples.
In my experience, I've met many stoners whose driving force is empathy and compassion and not narcissism and apathy.
Anyway, keep in mind any substance abuse is often an amplifier of issues that already existed.