Rich from gambling can be only gambling site owners. They can be really rich - a lot of Bitcoins.
You might be right. But OP asking us, by playing gambling, not providing the service of gambling house. If the gambling house owners also a gambler, then he might be a richest person in my guessing.
As long as we are gambling that can be considered, investing in a gambling house could be qualified in the topic IMO, and for me that is the most effective to be rich in gambling because we know for the fact that only when we are lucky will we can win in gambling and that does not happen all the time.