I could see a design like this working and becoming popular as long as it is highly efficient, sometimes I have visited the websites of different casinos and they take 30 to 60 seconds to load fully, and at the time I just thought that the website was loading slowly during that particular day, however after a few visits I realize that is in fact the loading speed of that website which is too slow for a casino, if this minimalist look is paired with very fast loading times then I could see people liking it.
If the problem is that the loading time of the website looks slow on certain days, I think it has something to do with the server it is using. Supposedly if the casino has started to develop and can get more visitors or can increase in one month, the casino needs to upgrade their servers to provide easy access to the casino site. This is one form of convenience that casinos must provide so that their members do not experience loading time problems.
And also there might have problem on the development too. They may use any large data file which may slow down the website and on the same time their data load capacity might be lower for which they may face loading problem on their site. They should solve the problem by contacting with the support team of the server.