The iPhone turned out to be the most walled garden smartphone as well (even compared to older designs that relied on Java ME), and it didn't exactly hurt them.
The more relevant question is, can Facebook in 2022 excite people as much as Apple did when riding on the height of the iPod/iTunes craze in 2007?
You are misunderstanding or wilfully ignoring the details. They talk about interoperability as a key part of how this will become reality, and the fact that no single company can realise this vision...
I am misunderstanding then. I am also probably willfully assuming Facebook will continue to operate as they have been — trying to steer all users to their site, keep them engaged on their site.
"You've got mail!" LOL