He is an old player, he played very well this year when he got the chance, he got injured quite frequently I have to say and Milan looked great when he played, however no matter how great he is, he is still an old player, dude is almost 40 years old.
I do not think that he would have any advantage owning a casino neither, let's assume that he bets against himself, well he can do that without owning a casino, let's assume that people on his website wagered on one side too much, let's say maybe he has to lose in order for him to win a lot of money, he could miss shots, but there are 10 other people, but let's assume he has to win, well he wants to win every game anyway. So I do not see "too much" problem here, but even if it is just too much, if he is making a lot of profit from this, he could simply retire, because he is already at that age anyway.
Your argument makes sense but there is a reason why the rules are there for a reason, he has a conflict of interest and in many occupations the way it deals with this is the same, you need to choose one or the other occupation and never both, a lawyer cannot at any moment take two different sides of the same case, he can only hear one side and the moment he does and receives payment he cannot even listen to the other side or he will have an unfair advantage and the same is happening here.