Trading generally is a skill set, but I don't know if gambling should be classified as a skill too.
Taking calculated risks (which is part of gambling) is a skill so I'd say it's more or less a skill. There's only a small fraction of people who know the game of gambling well.
There is no limit to how much you can earn as a trader, I have a trader that earns more than $4k just in a single profitable trade due to the amount of capital he uses to trade and he earns up to $20k in a month.
Certain things determine how much money you can earn from trading.
1. The ability to trade profitably.
2. The amount of capital used in trading.
Most people always underrate the impact capital has on trades. In as much as putting more capital on the line means that you can probably lose more, it also means that you can win more. I think this is why there's been an influx of prop firms in the space to provide capital for traders who feel they can do better if they have the right funding / capital for their trades.
I know traders that earns a lot more than that and they don't take much risks or lev because they use a huge capital already.