People (mostly Xbox stans) fall so easily for MS PR spins... When they say it's "sustainable" people assume they mean it's "profitable" but if it was profitable that's the word they would've used, MS always make sure to make any information that they think is positive public (that's why the CEO made sure to mention that Xbox sold more than PS5 for a few months on specific countries, after years and years of not saying anything).
Gamepass itself clearly isn't profitable and isn't going to be anytime soon, with Xbox games selling like shit it pretty much has to make up for all their massive development structure expense as well as all the money they need to pay third party devs to put their games on Gamepass.
If Gamepass is profitable imagine how profitable PS+ would have to be since Sony invests so much less resources in comparison and still has way more subscribers...
MS entire plan revolved around Gamepass not being profitable, that way their size and willingness to accept massive losses would've kept the competition away. Too bad that it turns out that Sony can compete with it with minimal effort, no day one games, they didn't even bother with making many of their own old games available yet it's already has better games than Gamepass.
Acquiring Bethesda Activision and Blizzard will only make the service even more unsustainable (unless they walk back of their word, wouldn't be the first time), regardless, I love to see it. Phil Spencer will go down as one of the biggest clowns and con artists in the game industry, well deserved.