You are partly right about that but I think its pretty safe to do this in a already existing casino website.
It can in my opinion be very profitable because this whole scene is upcoming.
Yes it is little bit risk to investing on other casino's but you can create your own casino if you have that much amount means yes if we have money we can make one team and we will create our own business so here profit and loss both will be in our side. Instead of this you can invest on other casinos means if they shut down there site means that's it gone everything.
By creating your own casino, you need to have at least a huge capital in order to finance the development and the marketing aspect, it is really not that simple as what we imagine. Now, if you do not have that resources to establish and online casino then the simple way to do is just to invest in other online casino and take part of their profit. Just remember to exercise caution in investing and put your money only on the trusted one.