I don't know how gambling and trading are linked together as you painted it, I just don't know. For me, they are not linked together, but have a certain thing in common, which is risk. I can assure you that good traders know what they are doing and manage their way to success, unlike gambling, which is highly luck-based. It's basically betting.
That aside. This is practical, those people whom I know who are gambling are still gambling, especially those who are core gamblers, despite losing far more than what they gained. But today, only a trader remains among the hundreds of traders I knew. This is the same everywhere. Hasn't that rung a bell that the addiction in gambling is not the same as that in trading?
You’re right to say that trading, especially well managed trading, is base on skills, while gambling is fully base on probability, which made it hard for individual to control their selves while gambling. Here is how you can differentiate them:
For Trading when involved properly:
1) Research and analysis (technical, fundamental, sentiment)
2) Strategy, discipline, and risk management (stop-losses, portfolio diversification)
3)Long-term growth perspectives (especially in long time investing)
For Gambling:
1) It involves pure chance or heavily stacked odds ( slot machines)
2) Has a negative expected value over time
3) Offers little room for informed decision making (unless in sports betting)
So trading can be skillful and repeatable, while gambling is mostly addictive and you can let go.
Furthermore, the only link that people draw between trading and gambling always comes from how some individuals approach trading like gambling, not from what the activities truly are. Like people that go into trading without basic knowledge this are people that always engage themselves in Over leveraging trades (like, 100x margin), Chasing losses or revenge trading, Trading with no strategy or risk management, Making impulsive decisions driven by emotions or hype
So, when people say “trading is gambling,” they are just referring to the bad traders not the disciplined, strategic traders.