You really believe it can't be successful until you see the numbers? Devs...Microsoft accountants don't count?
There are different metrics of successful. A mobile game like Miitomo can be considered a flop because of how little money it made, but also can be a success if its main goal was to get people to sign up for Nintendo Accounts and provide market and customer behavior data to Nintendo.
GamePass can be considered a success since its the biggest thing the Xbox plattform has going for itself and its a very attractive service - - yet they dont share sub numbers or how much money people are spending there, so we will never have the full story or see how the sub engagement level evolve over times.
I have nothing against calling GamePass a success or people loving the service, but the moment you start calling out other services and call them successful - it gets a bit shaky. Sony provides PSNow sub numbers - we know where the service started and how it evolved.
Devs ?
What about devs ? Of course no devs that is on GamePass and getting paid is gonna badmouth the service - what about the other devs that were more critical about that kind of service ? Or the devs that arent invited to the GamePass party but at the same dont stand a chance of selling their games anywhere close of the intended price because of GamePass and how it affect the gamer spending behavior.
For all we know everything might be just as perfect as it seems - but personally i couldnt really evaluate the success of a subscription service compared to other services without knowing how many subscribers we are even talking about - and more importantly how much they are spending. How big is that GamePass business ?
All im gonna say - we would likely get less of these kind of articles if all relevant data on GamePass were public and would force people to have some more critical takes on that business and realize why only MS can or is willing to provide such a service at this point.