I believe both of them are risky because you will bet your money with something that you are not sure about winning. The only difference is that in gambling if you lose you lose in trading if you are on lose and you do not sell your holdings then you still got the chance to wait for your money to come back to its value.
I still haven't found something known as skill based gambling. If we are needed to compare the address in both of these choices thus simply what I can say is that they are equally risky.
Trading doesn't require practice and the things to improve with time but gambling is all about luck and we could not change the scenario just with the passage of time by polishing our skills. In my opinion only sports betting is something that really offers definite winning if you have been into this since quite a long time.
Well I agree they both have equal amount of risk, but what I don't understand is your statement about trading, in my opinion trading require a lot of practice and training without that everything is useless, even though you follow other people trading plan in the end you gonna end up losing money because you didn't have experience with it.