The question is if Game Pass is profitable enough (especially considering it's increasingly the bread and butter of Xbox), or if Microsoft is keeping an unsustainable pricing strategy to try kill competition and will enshittify the service later (like YouTube for example)
They're making just under $3B/yr on Game Pass. It seems absolutely obvious that the vast majority of their costs will be game licensing. That's why they rotate games in and out so often.
For what it's worth, the same announcement about spending $1b/yr included a confirmation that the Game Pass is currently turning a profit.
It's not even a question anymore. Even if every single subscriber is on the highest tier, they're not even close to making back their third-party costs to run the service, let alone server costs, cannibalized first-party game sales, and whatever else they pay to run it.
They spend "a billion dollars a year supporting third-party games coming into Game Pass", not total (I know the headline says over a billion but it's still a bit misleading).