I’m not a high rank player so you may not agree with my words, but I doubt that Stake would rig player’s bet once they upgraded because if they did then they would have been out of business by now. Furthermore in a hypothetical scenario what if you continued to win more, then you would praise the site hence I feel you’re wrong to judge them in a negative way.
He isn't really judging them in a negative way to be honest. He simply expressed some genuine doubts which every gambler usually thinks of from time to time due to the random nature of gambling itself.
He even pointed out how his doubts were pointless later on. I felt the same way on multiple occasions in various gambling sites and cleared my doubts in a logical manner.