Sony didn't reverse fortunes, Microsoft did. No one bought an Xbone because of the worst reveal and launch run up in industry history. Sony swooped in and grabbed COD when they saw their opportunity, because they knew it would help grow their PSN. I'm sure Activision was only too happy to do it because PlayStation 4 quickly became the dominant platform basically from day one. Sony was bolstered by the fact that their chief competition was basically DOA, allowing them to establish PSN as the place to play - fuelled is no small part by COD, the dominant FPS multiplayer game. That's clearly not happening this generation.
When COD goes exclusive to Xbox, PlayStation will need another "best on PlayStation" juggernaut because COD's hardcore will follow their game.
COD on Game Pass, and exclusive to Xbox? Yeah, the COD casuals whose investment is only COD will absolutely trade in their PlayStations for Xboxes or pick up a cheap Series S to compliment their PS5s. Everything COD being on Game Pass means that, not only will COD be potentially cheaper for them, they'll have access to every COD title at once. You're failing to understand precisely how COD is as big as it is.