Gambling is very risky.If your luck is good then you can earn from gambling.If you lick is bad then you will lose.In Gambling you dont need to know anything.I didnt try forex but I saw few people who tried forex and if you have proper knowledge then forex is good. But I love crypto trading.Though I am not a professional trader nor expert trader.But I trade with most popular currency and wait for the profits.But also make a research before jump 
You trade with the most popular currency then wait for the profits? then you must be an investor rather than a trader.Gambling, Forex and Crypto trading is almost the same, for me, the only difference about these 3 are the percentage of winning and how well you'll initiate your strategy but at the end of the day you will be still needing a good amount of money to earn a decent amount of profit.
I agree with you about winning percentage as in gambling if you are doing casino betting then loosing chances are high, but if you are doing sports betting then profit is low but in ROI it is very profitable just like trading. so i think in this all three option you first need is the experience and bankroll system to invest so that you should be able to buy in more dip and take profit when it starts moving up.