I haven’t seen the movie, but it makes sense his gambling was a front for another method of making money.
I actually enjoyed the movie, and yes, the movie featured other money making schemes for which the main character had to create a lot of fronts to launder the money.
So far there is no discernible manner in which Stephen Paddock acquired all this money. All we see is him spending a lot, and all that is offered is this weak claim that he was a "professional gambler."
I think he was a professional smuggler, probably drugs from South of the border, and *THAT* is where the money comes from. The Gambling was to launder his money.
One does not consistently win when playing video poker against a machine.