I somewhat agree, but don't forget, those marketing investments need to be financed somehow. 
If the casino refuses to discuss the case publicly and goes through a mediator that decides against them, that's the only proof we have that they are wrong. Same thing if the mediator sides with the casino. Since they won't share any information publicly in 99% of the cases, there is no other way.
The mediation business is trust business. Once they build a reputation then they can start manipulating cases to benefit their business too. In a case between a regular client and a casino which has good relation with the mediator [he supposed to have, because mediation is his business], I do not see how the mediator will not be biased too.If the casino refuses to discuss the case publicly and goes through a mediator that decides against them, that's the only proof we have that they are wrong. Same thing if the mediator sides with the casino. Since they won't share any information publicly in 99% of the cases, there is no other way.
Everything is complicated, super subjective. A fair solution is to bring everything in the public area and let it decide openly but you, I and everyone know, they have an excuse that everyone will know their secrets which will risk their business. I have no idea what secrets it could be.
In a program if it is designed to add two numbers then it will always add two numbers. So what secret?
My argument is, I do not side for gambling business too. Ultimately it's down to the players how much he can afford to lose. Gambling businesses are protected by their shady terms and conditions. Going to a casino/sportsbook, placing few bets, spend $5, $10 or $100 is fine but when you are going there to spend thousands and expecting you are going to take the house down, then you are a fool. Whatever they gamble, all of these money are already in the debit side of your personal account.