Then why not Casinoguru request it to the casino instead of you if you have a lead that the Stake games really have a problem with their provably fair system because they will surely entertain you due to risk involved since Stake has a lot of customer.
Most probably he already brought up this case while the arbitrator itself instruct him to get more substantial evidence to prove his claim before they entertaining issue like this.
He is persistent on proving his conclusion while It’s odd that he can’t gain support by an arbitrator if he really have something solid.