Compare that to Rift Apart, which last I heard is more in the 1-2M sales range. Insomniac is a true triple-A studio, with more like 400-500 employees plus the full development support of PSS's shared resources. Ratchet & Clank is a more broadly known franchise, in a genre and aesthetic that is more age and demographic accessible.
Additionally, while this would equally affect Returnal & Rift Apart; PS5 shortages do dampen all PS5 exclusive game sales compared to more broadly available titles.
Within that context, it's clear to me that Returnal was a tremendous success. Not a Triple-A success, but its not all about raw sales at the end of the day. Cost to produce also needs to be considered.
To be clear: I absolutely believe Xbox isn't just "all triple-A all the time". They have the triple-A teams. They have the smaller teams (Maybe not Rare/Playground as they're huge nowadays, but: Ninja Theory, Compulsion, Double Fine, World's Edge, maybe even Obsidian, plus their exclusivity deals with Moon and Asobo). Its more-so a discussion about their recent acquisitions strategy.
Not really. Destiny has a smaller audience than CoD, and Activision Blizzard is a huge purchase with lots a of valuable IPs that go beyond CoD and can still grow (Bungie, OTOH, currently only has Destiny in it's catalog).
Bungie revenue was estimated around $300 million for 2019 vs. $6,5b for Activision Blizzard, so price seems to be in line for both purchases, around 8x annual rev.
Keep in mind Microsoft has bought ton of small studios as well! (Rare, Playground).
Returnal is a good title, but far from being a success by AAA standards (last time they reported sales of the game, in June 2021. it was 560.000 copies). I think part of the aura of success comes from being one of the very few exclusive titles created specifically for the PS5.