I think it is not wrong at all it is just a game that you will risk some money for a chance to earn some,
So I would only consider it as an Investment there are also some risk in investment just like in gambling.
Playing was the worst type of investment if you consider this as possible source of income. But investing on casino was another story, In that case for that can't be considered as sin. For me, No matter what we say and explanation about gambling, We can't please everybody but we based on Bible and other teachings, Gambling was obviously a sin because it is form of greediness, We risk our money just to have a fast income and without investing effort, Gambling just teaches us on how to become lazy.