I suspect gambling could have positive effects. It could help people manage money better and not give in to impulsive tendencies. There isn't a significant difference between gambling and investing. There is a degree of risk inherent in everything which can't be eliminated. The best we might hope for is to learn to mitigate that risk and that could take practice, which gambling could provide.
Yes, there is. A huge one. In gambling, the mathematical return of every bet is negative, whereas in investing you have not that mathematical certainty.
I think you example could only be applied to poker. People starting poker from zero and becoming successful develop abilities necessary in investing. But those people dont call themselves gamblers, they call bad players gamblers.
As for OP, I think problematic gambling behavior is a consequence of previous problems. Nobody sane, with a happy life and without problems, ends up gambling pathologically.