It also depends on how much high rollers are in the casinos and how unlucky the gamblers are (though this factor cannot be influenced). If the site has a lot of gamblers that bet big amounts then most likely your investment can earn a lot of money. If not then it would be a steady climb for you in that casino.
Yes you are right and I don't believe that all the time a casino will generate no profit. There will be times that there will be a lucky gambler that wins a lot but there would be a time of recovering for the management that will encounter a rage bettor and will bet almost all his funds till the end that will lead him in losing.